Window,
WindowProxy, and Location objectsWindow objectWindowProxy exotic objectHistory interfaceLocation interfacemultipart/x-mixed-replace resourcesThis section describes features that apply most directly to Web browsers. Having said that, except where specified otherwise, the requirements defined in this section do apply to all user agents, whether they are Web browsers or not.
A browsing context is an environment in which Document
objects are presented to the user.
A tab or window in a Web browser typically contains a browsing
context, as does an iframe or frames in a
frameset.
A browsing context has a corresponding WindowProxy object.
A browsing context has a session history, which lists the
Document objects that the browsing context has presented, is presenting,
or will present. At any time, one Document in each browsing context is
designated the active document.
A Document's browsing context is the browsing context
whose session history contains the Document, if any such browsing
context exists and has not been discarded.
In general, there is a 1-to-1 mapping from the Window object to the
Document object, as long as the Document object has a browsing context. There are two exceptions. First, a
Window can be reused for the presentation of a second Document in the
same browsing context, such that the mapping is then 1-to-2. This occurs when a
browsing context is navigated from the initial
about:blank Document to another, with replacement enabled.
Second, a Document can end up being reused for several Window objects
when the document.open() method is used, such that the
mapping is then many-to-1.
A Document does not necessarily have a browsing context associated with it. In particular, data
mining tools are likely to never instantiate browsing contexts. A Document created
using an API such as createDocument()
never has a browsing context. And the
Document originally created for an iframe element, which has since been
removed from the document, has no associated
browsing context, since that browsing context was discarded.
A browsing context can have a creator browsing context, the browsing context that was responsible for its creation. If a browsing context has a parent browsing context, then that is its creator browsing context. Otherwise, if the browsing context has an opener browsing context, then that is its creator browsing context. Otherwise, the browsing context has no creator browsing context.
If a browsing context context has a creator browsing context creator, it also has the following properties. In what follows, let creator document be creator's active document at the time context is created:
To create a new browsing context:
Let browsingContext be a new browsing context.
Call the JavaScript InitializeHostDefinedRealm() abstract operation with the following customizations:
For the global object, create a new Window object
window.
For the global this value, use browsingContext's
WindowProxy object.
Let realm execution context be the created JavaScript execution context.
Set up a browsing context environment settings object with realm execution context, and let settingsObject be the result.
Let document be a new Document, marked as an HTML document in quirks mode, whose content type is "text/html",
and which is both ready for post-load tasks and completely loaded
immediately.
Ensure that document has a single child html node, which itself
has two empty child nodes: a head element, and a body element.
Set window's associated
Document to document.
Set browsingContext's WindowProxy object's
[[Window]] internal slot
value to window.
The internal slot value is updated when navigations occur.
Set the origin of document:
If browsingContext has a creator browsing context, then the origin of document is the creator origin.
Otherwise, the origin of document is a unique opaque origin.
If browsingContext has a creator browsing context, then set document's referrer to the serialization of creator URL.
If browsingContext has a creator browsing context, then set document's referrer policy to the creator referrer policy.
Implement the sandboxing for document.
Set the allow* flags for document.
Set settingsObject's execution ready flag.
Add document to browsingContext's session history.
Return browsingContext.
Certain elements (for example, iframe elements) can instantiate further browsing contexts. These elements are called browsing
context containers.
Each browsing context container has a nested browsing context, which is either a browsing context or null.
If a browsing context is the nested browsing context of a browsing context container, then the browsing context is said to be nested through the browsing context container's node document.
A browsing context child is said to be a child browsing context of another browsing context parent, if all of the following conditions hold:
child is a nested browsing context of a browsing context container element
element is connected
element's shadow-including root's browsing context is parent
A browsing context child is then a document-tree child browsing context of parent if it is a child browsing context and its browsing context container is not just connected, but also in a document tree.
A browsing context child may have a parent browsing context. This is the unique browsing context that has child as a child browsing context, if any such browsing context exists. Otherwise, the browsing context has no parent browsing context.
A browsing context A is said to be an ancestor of a browsing context B if there exists a browsing context A' that is a child browsing context of A and that is itself an ancestor of B, or if the browsing context A is the parent browsing context of B.
A browsing context that is not a nested browsing context has no parent browsing context, and is the top-level browsing context of all the browsing contexts for which it is an ancestor browsing context.
The transitive closure of parent browsing contexts for a browsing context that is a nested browsing context gives the list of ancestor browsing contexts.
The list of the descendant browsing contexts of a Document d
is the (ordered) list returned by the following algorithm:
Let list be an empty list.
For each child browsing context of d that is nested through an element that is in
the Document d, in the tree order of the elements
nesting those browsing contexts, run these substeps:
Append that child browsing context to the list list.
Append the list of the descendant browsing contexts of the active document of that child browsing context to the list list.
Return the constructed list.
A Document is said to be fully
active when it has a browsing context and it is
the active document of that browsing context, and either its browsing
context is a top-level browsing context, or it has a parent browsing
context and the Document through which it is nested is itself
fully active.
Because they are associated with an element, child
browsing contexts are always tied to a specific Document in their parent
browsing context. User agents must not allow the user to interact with child browsing contexts of elements that are in Documents
that are not themselves fully active.
A browsing context that is a nested browsing context can be put into
a delaying load events mode. This is used when it is
navigated, to delay the load event of its
browsing context container before the new Document is created.
The document family of a browsing context consists of the union of all
the Document objects in that browsing context's session
history and the document families of all those
Document objects. The document family of a Document object
consists of the union of all the document families of the
browsing contexts that are nested through the Document object.
The content document of a browsing context container container is the result of the following algorithm:
If container's nested browsing context is null, then return null.
Let context be container's nested browsing context.
Let document be context's active document.
If document's origin and the origin specified by the current settings object are not same origin-domain, then return null.
Return document.
topReturns the WindowProxy for the top-level browsing context.
parentReturns the WindowProxy for the parent browsing context.
frameElementReturns the Element for the browsing context container.
Returns null if there isn't one, and in cross-origin situations.
The top IDL attribute, on getting, must run the
following algorithm:
Let windowProxy be this Window object's WindowProxy
object.
If there is no browsing context with windowProxy as its
WindowProxy object, then return null.
Let context be that browsing context.
If context is a top-level browsing context, then return
context's WindowProxy object.
Otherwise, context must have a top-level browsing context (i.e. an
ancestor browsing context with no parent browsing context). Return that
top-level browsing context's WindowProxy object.
The parent IDL attribute, on getting, must run the
following algorithm:
Let windowProxy be this Window object's WindowProxy
object.
If there is no browsing context with windowProxy as its
WindowProxy object, then return null.
Let context be that browsing context.
If context is a child browsing context of another browsing
context parent, then return parent's WindowProxy
object.
Otherwise, context must be a top-level browsing context. Return
context's WindowProxy object.
The frameElement IDL attribute, on getting,
must run the following algorithm:
Let windowProxy be this Window object's WindowProxy
object.
If there is no browsing context with windowProxy as its
WindowProxy object, then return null.
Let context be that browsing context.
If context is not a nested browsing context, then return null.
Let container be context's browsing context container.
If container's node document's origin is not same origin-domain with the current settings object's origin, then return null.
Return container.
An example of when these IDL attributes can return null is as follows:
<!DOCTYPE html>
<iframe></iframe>
<script>
"use strict";
const element = document.querySelector("iframe");
const iframeWindow = element.contentWindow;
element.remove();
console.assert(iframeWindow.top === null);
console.assert(iframeWindow.parent === null);
console.assert(iframeWindow.frameElement === null);
</script>
Here the browsing context corresponding to iframeWindow
was discarded when element was removed from the document.
It is possible to create new browsing contexts that are related to a top-level browsing context without being nested through an element. Such browsing contexts are called auxiliary browsing contexts. Auxiliary browsing contexts are always top-level browsing contexts.
An auxiliary browsing context has an opener browsing context, which is the browsing context from which the auxiliary browsing context was created.
The opener IDL attribute on the Window
object, on getting, must return the WindowProxy object of the browsing
context from which the current browsing context was created (its opener
browsing context), if there is one, if it is still available, and if the current
browsing context has not disowned its opener;
otherwise, it must return null. On setting, if the new value is null then the current
browsing context must disown its
opener; if the new value is anything else then the user agent must
call the [[DefineOwnProperty]] internal method of the Window object, passing the
property name "opener" as the property key, and the Property Descriptor {
[[Value]]: value, [[Writable]]: true, [[Enumerable]]: true,
[[Configurable]]: true } as the property descriptor,
where value is the new value.
If a browsing context has disowned its
opener, the value of its window.opener is null. That prevents scripts in the browsing context from changing
any properties of its opener browsing context's Window (i.e., the window
from which the browsing context was created).
Otherwise, if a browsing context has not disowned its
opener, then scripts in that browsing context can use window.opener to change properties of its opener browsing
context's Window. For example, a script running in the browsing
context can change the value of window.opener.location, causing the
opener browsing context to navigate to a completely different document.
A browsing context A is familiar with a second browsing context B if one of the following conditions is true:
A browsing context A is allowed to navigate a second browsing context B if the following algorithm terminates positively:
If A is not the same browsing context as B, and A is not one of the ancestor browsing contexts of B, and B is not a top-level browsing context, and A's active document's active sandboxing flag set has its sandboxed navigation browsing context flag set, then abort these steps negatively.
Otherwise, if B is a top-level browsing context, and is one of the ancestor browsing contexts of A, then:
If this algorithm is triggered by user activation and A's active document's active sandboxing flag set has its sandboxed top-level navigation with user activation browsing context flag set, then abort these steps negatively.
Otherwise, If this algorithm is not triggered by user activation and A's active document's active sandboxing flag set has its sandboxed top-level navigation without user activation browsing context flag set, then abort these steps negatively.
Otherwise, if B is a top-level browsing context, and is
neither A nor one of the ancestor
browsing contexts of A, and A's
Document's active sandboxing flag set has its sandboxed
navigation browsing context flag set, and A is not the one
permitted sandboxed navigator of B, then abort these steps
negatively.
Otherwise, terminate positively!
An element has a browsing context scope origin if its Document's
browsing context is a top-level browsing
context or if all of its Document's ancestor browsing contexts all have active
documents whose origin are the same origin as the element's
node document's origin. If an element has a browsing context scope
origin, then its value is the origin of the element's node
document.
Each browsing context is defined as having a list of one or more directly reachable browsing contexts. These are:
The transitive closure of all the browsing contexts that are directly reachable browsing contexts forms a unit of related browsing contexts.
Each unit of related browsing contexts is then further divided into the smallest
number of groups such that every member of each group has an active document with an
origin that, through appropriate manipulation of the document.domain attribute, could be made to be same
origin-domain with other members of the group, but could not be made the same as members of
any other group. Each such group is a unit of related similar-origin browsing
contexts.
There is also at most one event loop per unit of related similar-origin browsing contexts (though several units of related similar-origin browsing contexts can have a shared event loop).
Browsing contexts can have a browsing context name. Unless stated otherwise, it is the empty string.
A valid browsing context name is any string with at least one character that does not start with a U+005F LOW LINE character. (Names starting with an underscore are reserved for special keywords.)
A valid browsing context name or keyword is any string that is either a valid
browsing context name or that is an ASCII case-insensitive match for one of:
_blank, _self, _parent, or
_top.
These values have different meanings based on whether the page is sandboxed or not, as
summarized in the following (non-normative) table. In this table, "current" means the
browsing context that the link or script is in, "parent" means the parent
browsing context of the one the link or script is in, "top" means the top-level
browsing context of the one the link or script is in, "new" means a new top-level
browsing context or auxiliary browsing context is to be created, subject to
various user preferences and user agent policies, "none" means that nothing will happen, and
"maybe new" means the same as "new" if the "allow-popups" keyword is also specified on the
sandbox attribute (or if the user overrode the
sandboxing), and the same as "none" otherwise.
| Keyword | Ordinary effect | Effect in an iframe with...
| |
|---|---|---|---|
sandbox=""
| sandbox="allow-top-navigation"
| ||
| none specified, for links and form submissions | current | current | current |
| empty string | current | current | current |
_blank
| new | maybe new | maybe new |
_self
| current | current | current |
_parent if there isn't a parent
| current | current | current |
_parent if parent is also top
| parent/top | none | parent/top |
_parent if there is one and it's not top
| parent | none | none |
_top if top is current
| current | current | current |
_top if top is not current
| top | none | top |
| name that doesn't exist | new | maybe new | maybe new |
| name that exists and is a descendant | specified descendant | specified descendant | specified descendant |
| name that exists and is current | current | current | current |
| name that exists and is an ancestor that is top | specified ancestor | none | specified ancestor/top |
| name that exists and is an ancestor that is not top | specified ancestor | none | none |
| other name that exists with common top | specified | none | none |
| name that exists with different top, if familiar and one permitted sandboxed navigator | specified | specified | specified |
| name that exists with different top, if familiar but not one permitted sandboxed navigator | specified | none | none |
| name that exists with different top, not familiar | new | maybe new | maybe new |
Most of the restrictions on sandboxed browsing contexts are applied by other algorithms, e.g. the navigation algorithm, not the rules for choosing a browsing context given a browsing context name given below.
The rules for choosing a browsing context given a browsing context name are as follows. The rules assume that they are being applied in the context of a browsing context, as part of the execution of a task.
If the given browsing context name is the empty string or _self, then
the chosen browsing context must be the current one.
If the given browsing context name is _parent, then the chosen
browsing context must be the parent browsing context of the current one,
unless there isn't one, in which case the chosen browsing context must be the current browsing
context.
If the given browsing context name is _top, then the chosen browsing
context must be the top-level browsing context of the current one, if there is one,
or else the current browsing context.
If the given browsing context name is not _blank and there exists a
browsing context whose name is the same as the given
browsing context name, and the current browsing context is familiar with that
browsing context, and the user agent determines that the two browsing contexts are related
enough that it is ok if they reach each other, then that browsing context must be the chosen
one. If there are multiple matching browsing contexts, the user agent should select one in some
arbitrary consistent manner, such as the most recently opened, most recently focused, or more
closely related.
Otherwise, a new browsing context is being requested, and what happens depends on the user agent's configuration and abilities — it is determined by the rules given for the first applicable option from the following list:
There is no chosen browsing context. The user agent may inform the user that a popup has been blocked.
Typically, there is no chosen browsing context.
The user agent may offer to create a new top-level browsing context or reuse an existing top-level browsing context. If the user picks one of those options, then the designated browsing context must be the chosen one (the browsing context's name isn't set to the given browsing context name). The default behavior (if the user agent doesn't offer the option to the user, or if the user declines to allow a browsing context to be used) must be that there must not be a chosen browsing context.
If this case occurs, it means that an author has explicitly sandboxed the document that is trying to open a link.
A new auxiliary browsing context must be created, with the opener
browsing context being the current one. If the given browsing context name is not
_blank, then the new auxiliary browsing context's name must be the
given browsing context name (otherwise, it has no name). The chosen browsing context must be
this new browsing context.
If the newly created browsing context is immediately navigated, then the navigation will be done with replacement enabled.
The chosen browsing context is the current browsing context.
There must not be a chosen browsing context.
User agent implementors are encouraged to provide a way for users to configure the user agent to always reuse the current browsing context.
If the chosen browsing context picked above, if any, is a new browsing context, then:
Let flagSet be the current browsing context's active document's active sandboxing flag set.
If flagSet's sandboxed navigation browsing context flag is set, then the current browsing context must be set as the new browsing context's one permitted sandboxed navigator.
If flagSet's sandbox propagates to auxiliary browsing contexts flag is set, then all the flags that are set in flagSet must be set in the new browsing context's popup sandboxing flag set.
When the user agent is required to set up a browsing context environment settings object, given a JavaScript execution context execution context and an optional environment reserved environment, it must run the following steps:
Let realm be the value of execution context's Realm component.
Let window be realm's global object.
Let url be a copy of the URL of
window's associated
Document.
Let settings object be a new environment settings object whose algorithms are defined as follows:
Return execution context.
Return the module map of
window's associated
Document.
Return the browsing context with which window is associated.
Return the event loop that is associated with the unit of related similar-origin browsing contexts to which window's browsing context belongs.
Return window's associated
Document.
Return the current character encoding
of window's associated
Document.
Return the current base URL of window's
associated Document.
Return the origin of window's associated Document.
Return the HTTPS state of
window's associated
Document.
Let document be the Document with which window is
currently associated.
While document is an iframe
srcdoc document and document's
referrer policy is the empty
string, set document to document's
browsing context's
browsing context container's node document.
Return document's referrer policy.
If reserved environment is given, then:
Set settings object's id to reserved environment's id, settings object's creation URL to reserved environment's creation URL, settings object's target browsing context to reserved environment's target browsing context, and settings object's active service worker to reserved environment's active service worker.
Set reserved environment's id to the empty string.
The identity of the reserved environment is considered to be fully transferred to the created environment settings object. The reserved environment is not searchable by the environment’s id from this point on.
Otherwise, set settings object's id to a new unique opaque string, settings object's creation URL to url, settings object's target browsing context to null, and settings object's active service worker to null.
Set realm's [[HostDefined]] field to settings object.
Return settings object.
Window,
WindowProxy, and Location objectsAlthough typically objects cannot be accessed across origins, the web platform would not be true to itself if it did not have some legacy exceptions to that rule that the web depends upon.
When perform a security check is invoked, with a platformObject, identifier, and type, run these steps:
If platformObject is a Window or Location object,
then:
Repeat for each e that is an element of CrossOriginProperties(platformObject):
If SameValue(e.[[Property]], identifier) is true, then:
If type is "method" and e has neither
[[NeedsGet]] nor [[NeedsSet]], then return.
Otherwise, if type is "getter" and
e.[[NeedsGet]] is true, then return.
Otherwise, if type is "setter" and
e.[[NeedsSet]] is true, then return.
If IsPlatformObjectSameOrigin(platformObject) is false, then throw
a "SecurityError" DOMException.
Window and Location objects both have a
[[CrossOriginPropertyDescriptorMap]] internal slot, whose value is initially an empty
map.
The [[CrossOriginPropertyDescriptorMap]] internal slot contains a map
with entries whose keys are (currentGlobal, objectGlobal,
propertyKey)-tuples and values are property descriptors, as a memoization of what is
visible to scripts when currentGlobal inspects a Window or
Location object from objectGlobal. It is filled lazily by
CrossOriginGetOwnPropertyHelper, which consults it on future lookups.
User agents should allow a value held in the map to be garbage collected along with its corresponding key when nothing holds a reference to any part of the value. That is, as long as garbage collection is not observable.
For example, with const href =
Object.getOwnPropertyDescriptor(crossOriginLocation, "href").set the value and its
corresponding key in the map cannot be garbage collected as that would be observable.
User agents may have an optimization whereby they remove key-value pairs from the map when
document.domain is set. This is not observable as document.domain cannot revisit an earlier value.
For example, setting document.domain
to "example.com" on www.example.com means user agents can remove all
key-value pairs from the map where part of the key is www.example.com, as that can never be part
of the origin again and therefore the corresponding value could never be retrieved
from the map.
If O is a Location object, then return «
{ [[Property]]: "href", [[NeedsGet]]: false, [[NeedsSet]]: true },
{ [[Property]]: "replace" } ».
Let crossOriginWindowProperties be «
{ [[Property]]: "window", [[NeedsGet]]: true, [[NeedsSet]]: false },
{ [[Property]]: "self", [[NeedsGet]]: true, [[NeedsSet]]: false },
{ [[Property]]: "location", [[NeedsGet]]: true, [[NeedsSet]]: true },
{ [[Property]]: "close" },
{ [[Property]]: "closed", [[NeedsGet]]: true, [[NeedsSet]]: false },
{ [[Property]]: "focus" },
{ [[Property]]: "blur" },
{ [[Property]]: "frames", [[NeedsGet]]: true, [[NeedsSet]]: false },
{ [[Property]]: "length", [[NeedsGet]]: true, [[NeedsSet]]: false },
{ [[Property]]: "top", [[NeedsGet]]: true, [[NeedsSet]]: false },
{ [[Property]]: "opener", [[NeedsGet]]: true, [[NeedsSet]]: false },
{ [[Property]]: "parent", [[NeedsGet]]: true, [[NeedsSet]]: false },
{ [[Property]]: "postMessage" } ».
Repeat for each e that is an element of O's document-tree child browsing context name property set:
Add { [[Property]]: e } as the last element of crossOriginWindowProperties.
Return crossOriginWindowProperties.
Indexed properties do not need to be safelisted as they are handled directly by
the WindowProxy object.
Return true if the current settings object's origin is same origin-domain with O's relevant settings object's origin, and false otherwise.
If this abstract operation returns undefined and there is no custom behavior, the
caller needs to throw a "SecurityError" DOMException.
If P is @@toStringTag, @@hasInstance, or @@isConcatSpreadable, then return PropertyDescriptor{ [[Value]]: undefined, [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.
Let crossOriginKey be a tuple consisting of the current settings object, O's relevant settings object, and P.
Repeat for each e that is an element of CrossOriginProperties(O):
If SameValue(e.[[Property]], P) is true, then:
If the value of the [[CrossOriginPropertyDescriptorMap]] internal slot of O contains an entry whose key is crossOriginKey, then return that entry's value.
Let originalDesc be OrdinaryGetOwnProperty(O, P).
Let crossOriginDesc be undefined.
If e.[[NeedsGet]] and e.[[NeedsSet]] are absent, then:
Let value be originalDesc.[[Value]].
If IsCallable(value) is true, then set value to an anonymous built-in function, created in the current Realm Record, that performs the same steps as the IDL operation P on object O.
Set crossOriginDesc to PropertyDescriptor{ [[Value]]: value, [[Enumerable]]: false, [[Writable]]: false, [[Configurable]]: true }.
Otherwise:
Let crossOriginGet be undefined.
If e.[[NeedsGet]] is true, then set crossOriginGet to an anonymous built-in function, created in the current Realm Record, that performs the same steps as the getter of the IDL attribute P on object O.
Let crossOriginSet be undefined.
If e.[[NeedsSet]] is true, then set crossOriginSet to an anonymous built-in function, created in the current Realm Record, that performs the same steps as the setter of the IDL attribute P on object O.
Set crossOriginDesc to PropertyDescriptor{ [[Get]]: crossOriginGet, [[Set]]: crossOriginSet, [[Enumerable]]: false, [[Configurable]]: true }.
Create an entry in the value of the [[CrossOriginPropertyDescriptorMap]] internal slot of O with key crossOriginKey and value crossOriginDesc.
Return crossOriginDesc.
Return undefined.
The reason that the property descriptors produced here are configurable is to preserve the invariants of the essential internal methods required by the JavaScript specification. In particular, since the value of the property can change as a consequence of navigation, it is required that the property be configurable. (However, see tc39/ecma262 issue #672 and references to it elsewhere in this specification for cases where we are not able to preserve these invariants, for compatibility with existing Web content.) [JAVASCRIPT]
Let desc be ? O.[[GetOwnProperty]](P).
Assert: desc is not undefined.
If IsDataDescriptor(desc) is true, then return desc.[[Value]].
Assert: IsAccessorDescriptor(desc) is true.
Let getter be desc.[[Get]].
If getter is undefined, throw a "SecurityError"
DOMException.
Return ? Call(getter, Receiver).
Let desc be ? O.[[GetOwnProperty]](P).
Assert: desc is not undefined.
If desc.[[Set]] is present and its value is not undefined, then:
Perform ? Call(setter, Receiver, «V»).
Return true.
Throw a "SecurityError" DOMException.
Let keys be a new empty List.
Repeat for each e that is an element of CrossOriginProperties(O):
Add e.[[Property]] as the last element of keys.
Return the concatenation of keys and « @@toStringTag, @@hasInstance, @@isConcatSpreadable ».
Window object[PrimaryGlobal, LegacyUnenumerableNamedProperties]
interface Window : EventTarget {
// the current browsing context
[Unforgeable] readonly attribute WindowProxy window;
[Replaceable] readonly attribute WindowProxy self;
[Unforgeable] readonly attribute Document document;
attribute DOMString name;
[PutForwards=href, Unforgeable] readonly attribute Location location;
readonly attribute History history;
readonly attribute CustomElementRegistry customElements;
[Replaceable] readonly attribute BarProp locationbar;
[Replaceable] readonly attribute BarProp menubar;
[Replaceable] readonly attribute BarProp personalbar;
[Replaceable] readonly attribute BarProp scrollbars;
[Replaceable] readonly attribute BarProp statusbar;
[Replaceable] readonly attribute BarProp toolbar;
attribute DOMString status;
void close();
readonly attribute boolean closed;
void stop();
void focus();
void blur();
// other browsing contexts
[Replaceable] readonly attribute WindowProxy frames;
[Replaceable] readonly attribute unsigned long length;
[Unforgeable] readonly attribute WindowProxy? top;
attribute any opener;
[Replaceable] readonly attribute WindowProxy? parent;
readonly attribute Element? frameElement;
WindowProxy? open(optional USVString url = "about:blank", optional DOMString target = "_blank", [TreatNullAs=EmptyString] optional DOMString features = "");
getter object (DOMString name);
// Since this is the global object, the IDL named getter adds a NamedPropertiesObject exotic
// object on the prototype chain. Indeed, this does not make the global object an exotic object.
// Indexed access is taken care of by the WindowProxy exotic object.
// the user agent
readonly attribute Navigator navigator;
readonly attribute ApplicationCache applicationCache;
// user prompts
void alert();
void alert(DOMString message);
boolean confirm(optional DOMString message = "");
DOMString? prompt(optional DOMString message = "", optional DOMString default = "");
void print();
unsigned long requestAnimationFrame(FrameRequestCallback callback);
void cancelAnimationFrame(unsigned long handle);
void postMessage(any message, USVString targetOrigin, optional sequence<object> transfer = []);
};
Window implements GlobalEventHandlers;
Window implements WindowEventHandlers;
callback FrameRequestCallback = void (DOMHighResTimeStamp time);
windowframesselfThese attributes all return window.
documentReturns the Document associated with window.
defaultViewReturns the Window object of the active document.
The Window has an associated
Document, which is a Document object. It is set when the
Window object is created, and only ever changed during navigation from the initial about:blank
Document.
The window, frames, and self IDL
attributes, on getting, must all return this Window object's browsing
context's WindowProxy object.
The document IDL attribute, on getting, must
return this Window object's associated
Document.
The Document object associated with a Window object can
change in exactly one case: when the navigate algorithm initializes a new Document object for the first page loaded
in a browsing context. In that specific case, the Window object of the
original about:blank page is reused and gets a new Document object.
The defaultView IDL attribute of the
Document interface, on getting, must return this Document's browsing context's WindowProxy object, if this
Document has an associated browsing context, or null otherwise.
For historical reasons, Window objects must also have a writable, configurable,
non-enumerable property named HTMLDocument whose value is the
Document interface object.
open( [ url [, target [, features ] ] ] )Opens a window to show url (defaults to about:blank), and returns it.
The target argument gives the name of the new window. If a window exists with that
name already, it is reused. The features argument can be
used to influence the rendering of the new window.
name [ = value ]Returns the name of the window.
Can be set, to change the name.
close()Closes the window.
closedReturns true if the window has been closed, false otherwise.
stop()Cancels the document load.
The open(url, target,
features) method on Window objects provides a mechanism for
navigating an existing browsing context or opening and
navigating an auxiliary browsing context.
When the method is invoked, the user agent must run the following steps:
Let entry settings be the entry settings object.
Let source browsing context be the responsible browsing context specified by entry settings.
If target is the empty string, let it be the string "_blank" instead.
If the user has indicated a preference for which browsing context to navigate, follow these substeps:
Let target browsing context be the browsing context indicated by the user.
If target browsing context is a new top-level browsing context, let the source browsing context be set as target browsing context's one permitted sandboxed navigator.
For example, suppose there is a user agent that supports control-clicking a
link to open it in a new tab. If a user clicks in that user agent on an element whose onclick handler uses the window.open() API to open a page in an iframe, but, while doing so,
holds the control key down, the user agent could override the selection of the target browsing
context to instead target a new tab.
Otherwise, apply the rules for choosing a browsing context given a browsing context name using target as the name and source browsing context as the context in which the algorithm is executed. If this results in there not being a chosen browsing context, then return null. Otherwise, let target browsing context be the browsing context so obtained.
If target browsing context was just created, either as part of the rules for choosing a browsing context given a browsing context name or due to the user indicating a preference for navigating a new top-level browsing context, then let new be true. Otherwise, let it be false.
Interpret features as defined in the CSSOM View specification. [CSSOMVIEW]
If url is the empty string, run the appropriate steps from the following list:
Jump to the step labeled end.
Let resource be the URL "about:blank".
Otherwise, parse url relative to entry settings, and let resource be the resulting URL record, if any. If the parse a URL algorithm failed, then run one of the following two steps instead:
Let resource be a resource representing an inline error page.
If new is false, jump to the step labeled end, otherwise, let
resource be the URL "about:blank".
If resource is "about:blank" and new is true, then
queue a task to fire an event named load at target browsing context's Window
object, with legacy target override flag set.
Otherwise, navigate target browsing context to resource, with the exceptions enabled flag set. If new is true, then replacement must be enabled. The source browsing context is source browsing context. Rethrow any exceptions.
End:
If the result of splitting features
on commas contains the token "noopener", then disown target browsing context's opener and
return null.
Otherwise, return the WindowProxy object of target browsing
context.
The name attribute of the Window object
must, on getting, return the current name of the
browsing context; and, on setting, set the name of the browsing context to the new value.
The name gets reset when the browsing context is navigated to another origin.
The close() method on Window
objects should, if all the following conditions are met, close the browsing context A:
A browsing context is script-closable if it is an auxiliary
browsing context that was created by a script (as opposed to by an action of the user), or
if it is a top-level browsing context whose session history contains
only one Document.
The closed attribute on Window
objects must return true if the Window object's browsing context has
been discarded, and false otherwise.
The stop() method on Window
objects should, if there is an existing attempt to navigate the browsing
context and that attempt is not currently running the unload a document
algorithm, cancel that navigation; then, it must abort the active document of the browsing
context of the Window object on which it was invoked.
lengthReturns the number of document-tree child browsing contexts.
Returns the indicated document-tree child browsing context.
The number of document-tree child browsing
contexts of a Window object W is the number of document-tree child browsing contexts of
W's associated Document's
browsing context.
The length IDL attribute's getter must return the
number of document-tree child browsing contexts of this Window
object.
Indexed access to document-tree child browsing contexts is defined through the [[GetOwnProperty]] internal method of the
WindowProxy object.
Window objectReturns the indicated element or collection of elements.
As a general rule, relying on this will lead to brittle code. Which IDs end up mapping to
this API can vary over time, as new features are added to the Web platform, for example. Instead
of this, use document.getElementById() or document.querySelector().
The document-tree child browsing context
name property set of a Window object window is the return value of
running these steps:
Let activeDocument be window's browsing context's active document.
Let childBrowsingContexts be all document-tree child browsing contexts of activeDocument's browsing context whose browsing context name is not the empty string, in order, and including only the first document-tree child browsing context with a given name if multiple document-tree child browsing contexts have the same one.
Remove each browsing context from childBrowsingContexts whose
active document's origin is not same origin with
activeDocument's origin and whose browsing context name does
not match the name of its browsing context container's name
content attribute value.
Return the browsing context names of childBrowsingContexts, in the same order.
This means that in the following example, hosted on https://example.org/, assuming https://elsewhere.example/
sets window.name to "spices", evaluating
window.spices after everything has loaded will yield undefined:
<iframe src=https://elsewhere.example.com/></iframe> <iframe name=spices></iframe>
The Window object supports named
properties. The supported property names of a Window object
window at any moment consist of the following, in tree order according to
the element that contributed them, ignoring later duplicates:
window's document-tree child browsing context name property set;
the value of the name content attribute for all
applet, embed, form, frameset,
img, and object elements that have a non-empty name content attribute and are in a document tree with
window's browsing context's active document as their
root; and
the value of the id content attribute for all HTML
elements that have a non-empty id content attribute and are
in a document tree with window's browsing context's
active document as their root.
To determine the value of a named property
name in a Window, the user agent must return the value obtained using the
following steps:
Let objects be the list of named objects with the name name.
There will be at least one such object, by definition.
If objects contains a nested browsing context, then return
the WindowProxy object of the nested browsing context corresponding to
the first browsing context container in tree order whose
nested browsing context is in objects, and abort these steps.
Otherwise, if objects has only one element, return that element and abort these steps.
Otherwise return an HTMLCollection rooted at the Document node,
whose filter matches only named objects with
the name name. (By definition, these will all be elements.)
Named objects with the name name, for the purposes of the above algorithm, consist of the following:
document-tree child browsing contexts of the active document whose name is name;
a, applet, area, embed,
form, frameset, img, or object elements that
have a name content attribute whose value is name and are
in a document tree with the active document as their
root; and
HTML elements that have an id content attribute
whose value is name and are in a document tree with the active
document as their root.
A browsing context has a strong reference to each of its Documents
and its WindowProxy object, and the user agent itself has a strong reference to its
top-level browsing contexts.
A Document has a strong reference to its Window object.
A Window object has a strong
reference to its Document object through its document attribute. Thus, references from other scripts to either of
those objects will keep both alive. Similarly, both Document and Window
objects have implied strong references to the
WindowProxy object.
Each script has a strong reference to its settings object, and each environment settings object has strong references to its global object, responsible browsing context, and responsible document (if any).
When a browsing context is to discard a
Document, the user agent must run the following steps:
Set the Document's salvageable state to false.
Run any unloading document cleanup steps for the Document that
are defined by this specification and other applicable specifications.
Remove any tasks associated with the
Document in any task source, without running those tasks.
Discard all the child browsing contexts of the Document.
Lose the strong reference from the Document's browsing context to the Document.
Whenever a Document object is discarded, it is also removed from the list of the worker's
Documents of each worker whose list contains that Document.
When a browsing context is discarded, the strong reference
from the user agent itself to the browsing context must be severed, and all the
Document objects for all the entries in the browsing context's session
history must be discarded as well.
User agents may discard top-level browsing contexts at any time (typically, in
response to user requests, e.g. when a user force-closes a window containing one or more top-level browsing contexts). Other browsing contexts must be discarded once their
WindowProxy object is eligible for garbage collection, in addition to the other
places where this specification requires them to be discarded.
A WindowProxy does not have a strong reference to the browsing
context it was created alongside. In particular, it is possible for a nested
browsing context to be discarded even
if JavaScript code holds a reference to its WindowProxy object.
When the user agent is required to close a browsing context, it must run the following steps:
Let specified browsing context be the browsing context being closed.
Prompt to unload the active document of the specified browsing context. If the user refused to allow the document to be unloaded, then abort these steps.
Unload the active document of the specified browsing context with the recycle parameter set to false.
Remove the specified browsing context from the user interface (e.g. close or hide its tab in a tabbed browser).
Discard the specified browsing context.
User agents should offer users the ability to arbitrarily close any top-level browsing context.
To allow Web pages to integrate with Web browsers, certain Web browser interface elements are exposed in a limited way to scripts in Web pages.
Each interface element is represented by a BarProp object:
interface BarProp {
readonly attribute boolean visible;
};
locationbar . visibleReturns true if the location bar is visible; otherwise, returns false.
menubar . visibleReturns true if the menu bar is visible; otherwise, returns false.
personalbar . visibleReturns true if the personal bar is visible; otherwise, returns false.
scrollbars . visibleReturns true if the scroll bars are visible; otherwise, returns false.
statusbar . visibleReturns true if the status bar is visible; otherwise, returns false.
toolbar . visibleReturns true if the toolbar is visible; otherwise, returns false.
The visible attribute, on getting, must return either true or a value determined by the user agent to most accurately represent the visibility state of the user interface element that the object represents, as described below.
The following BarProp objects exist for each Document object in a
browsing context. Some of the user interface elements represented by these objects
might have no equivalent in some user agents; for those user agents, except when otherwise
specified, the object must act as if it was present and visible (i.e. its visible attribute must return true).
BarProp objectBarProp objectBarProp objectBarProp objectBarProp objectvisible attribute may return false).BarProp objectvisible attribute may return
false).The locationbar attribute must return
the location bar BarProp object.
The menubar attribute must return the
menu bar BarProp object.
The personalbar attribute must return
the personal bar BarProp object.
The scrollbars attribute must return
the scrollbar BarProp object.
The statusbar attribute must return
the status bar BarProp object.
The toolbar attribute must return the
toolbar BarProp object.
For historical reasons, the status attribute
on the Window object must, on getting, return the last string it was set to, and on
setting, must set itself to the new value. When the Window object is created, the
attribute must be set to the empty string. It does not do anything else.
WindowProxy exotic objectA WindowProxy is an exotic
object that wraps a Window ordinary object, indirecting most operations through to
the wrapped object. Each browsing context has an associated WindowProxy
object. When the browsing context is navigated, the
Window object wrapped by the browsing context's associated
WindowProxy object is changed.
There is no WindowProxy interface object.
Every WindowProxy object has a
[[Window]] internal slot representing the wrapped
Window object.
The WindowProxy object internal methods are described in the subsections
below.
Although WindowProxy is named as a "proxy", it does not do
polymorphic dispatch on its target's internal methods as a real proxy would, due to a desire to
reuse machinery between WindowProxy and Location objects. As long as the
Window object remains an ordinary object this is unobservable and can be implemented
either way.
Let W be the value of the [[Window]] internal slot of this.
If IsPlatformObjectSameOrigin(W) is true, then return ! OrdinaryGetPrototypeOf(W).
Return null.
Return false.
Return true.
Return false.
Let W be the value of the [[Window]] internal slot of this.
If P is an array index property name, then:
Let index be ToUint32(P).
Let maxProperties be the number of document-tree child browsing contexts of W.
Let value be undefined.
If maxProperties is greater than 0 and index is less than maxProperties, then:
Let document be W's associated Document.
Set value to the WindowProxy object of the indexth
document-tree child browsing context of document's browsing context, sorted in the order
that their browsing context container
elements were most recently inserted into document, the
WindowProxy object of the most recently inserted browsing context
container's nested browsing context being last.
Return PropertyDescriptor{ [[Value]]: value, [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.
If IsPlatformObjectSameOrigin(W) is true, then return OrdinaryGetOwnProperty(W, P).
This is a willful violation of the JavaScript specification's invariants of the essential internal methods to maintain compatibility with existing Web content. See tc39/ecma262 issue #672 for more information. [JAVASCRIPT]
Let property be CrossOriginGetOwnPropertyHelper(W, P).
If property is not undefined, return property.
If property is undefined and P is in W's document-tree child browsing context name property set, then:
Let value be the WindowProxy object of the
named object with the name P.
Return PropertyDescriptor{ [[Value]]: value, [[Enumerable]]: false, [[Writable]]: false, [[Configurable]]: true }.
Throw a "SecurityError" DOMException.
Let W be the value of the [[Window]] internal slot of this.
If IsPlatformObjectSameOrigin(W) is true, then:
If P is an array index property name, return false.
Return ? OrdinaryDefineOwnProperty(W, P, Desc).
This is a willful violation of the JavaScript specification's invariants of the essential internal methods to maintain compatibility with existing Web content. See tc39/ecma262 issue #672 for more information. [JAVASCRIPT]
Throw a "SecurityError" DOMException.
Let W be the value of the [[Window]] internal slot of this.
If IsPlatformObjectSameOrigin(W) is true, then return ? OrdinaryGet(this, P, Receiver).
Return ? CrossOriginGet(this, P, Receiver).
Let W be the value of the [[Window]] internal slot of this.
If IsPlatformObjectSameOrigin(W) is true, then return ? OrdinarySet(W, this, Receiver).
Return ? CrossOriginSet(this, P, V, Receiver).
Let W be the value of the [[Window]] internal slot of this.
If IsPlatformObjectSameOrigin(W) is true, then:
If P is an array index property name, then return false.
Return ? OrdinaryDelete(W, P).
Throw a "SecurityError" DOMException.
Let W be the value of the [[Window]] internal slot of this.
Let keys be a new empty List.
Let maxProperties be the number of document-tree child browsing contexts of W.
Let index be 0.
Repeat while index < maxProperties,
Add ! ToString(index) as the last element of keys.
Increment index by 1.
If IsPlatformObjectSameOrigin(W) is true, then return the concatenation of keys and ! OrdinaryOwnPropertyKeys(W).
Return the concatenation of keys and ! CrossOriginOwnPropertyKeys(W).
Spec bugs: 28374
Origins are the fundamental currency of the Web's security model. Two actors in the Web platform that share an origin are assumed to trust each other and to have the same authority. Actors with differing origins are considered potentially hostile versus each other, and are isolated from each other to varying degrees.
For example, if Example Bank's Web site, hosted at bank.example.com, tries to examine the DOM of Example Charity's Web site, hosted
at charity.example.org, a "SecurityError"
DOMException will be raised.
An origin is one of the following:
An internal value, with no serialization it can be recreated from (it is serialized as
"null" per ASCII serialization of an origin), for which the
only meaningful operation is testing for equality.
A tuple consists of:
Origins can be shared, e.g., among multiple
Document objects. Furthermore, origins are generally
immutable. Only the domain of a tuple origin can be changed, and only through the document.domain API.
The effective domain of an origin origin is computed as follows:
If origin is an opaque origin, then return null.
If origin's domain is non-null, then return origin's domain.
Return origin's host.
Various specification objects are defined to have an origin. These origins are determined as follows:
Document objectsDocument's active sandboxing flag set
has its sandboxed origin browsing context flag setDocument was generated from a data: URLA unique opaque origin assigned when the
Document is created.
Document's URL's scheme is a network schemeA copy of the Document's URL's
origin assigned when the Document is
created.
The document.open() method can change
the Document's URL to
"about:blank". Therefore the origin is assigned when the
Document is created.
Document is the initial "about:blank" documentThe one it was assigned when its browsing context was created.
Document is a non-initial "about:blank" documentThe origin of the incumbent settings object when the navigate algorithm was invoked, or, if no script was involved, the origin of the node document of the element that initiated the navigation to that URL.
Document was created as part of the processing for javascript: URLsThe origin of the active document of the browsing context being navigated when the navigate algorithm was invoked.
Document is an iframe srcdoc documentThe origin of the Document's browsing context's browsing context
container's node document.
Document was obtained in some other manner (e.g. a Document
created using the createDocument()
API, etc)The default behavior as defined in the WHATWG DOM standard applies. [DOM].
The origin is a unique opaque origin assigned when the Document is
created.
img elementsA unique opaque origin assigned when the image is created.
The img element's node document's
origin.
audio and video elementsA unique opaque origin assigned when the media data is fetched.
The media element's node document's origin.
Other specifications can override the above definitions by themselves specifying the origin of
a particular Document object, image, or media element.
The Unicode serialization of an origin is the string obtained by applying the following algorithm to the given origin origin:
If origin is an opaque origin, then
return "null".
Let host be origin's host.
Let unicodeHost be host if host is not a domain, and the result of applying domain to Unicode to host otherwise.
Let unicodeOrigin be a new tuple origin consisting origin's scheme, unicodeHost, and origin's port.
Return the ASCII serialization of an origin, given unicodeOrigin.
The name ASCII serialization of an origin is misleading, as it merely serializes an origin, which are all ASCII by default due to the URL parser.
The Unicode
serialization of ("https", "xn--maraa-rta.example", null, null) is "https://maraña.example".
The ASCII serialization of an origin is the string obtained by applying the following algorithm to the given origin origin:
If origin is an opaque origin, then
return "null".
Otherwise, let result be origin's scheme.
Append "://" to result.
Append origin's host, serialized, to result.
If origin's port is non-null, append a U+003A COLON character (:), and origin's port, serialized, to result.
Return result.
Two origins, A and B, are said to be same origin if the following algorithm returns true:
If A and B are the same opaque origin, then return true.
If A and B are both tuple origins and their schemes, hosts, and port are identical, then return true.
Return false.
Two origins, A and B, are said to be same origin-domain if the following algorithm returns true:
If A and B are the same opaque origin, then return true.
If A and B are both tuple origins, run these substeps:
If A and B's schemes are identical, and their domains are identical and non-null, then return true.
Otherwise, if A and B are same origin and their domains are identical and null, then return true.
Return false.
| A | B | same origin | same origin-domain |
|---|---|---|---|
("https", "example.org", null, null)
| ("https", "example.org", null, null)
| ✅ | ✅ |
("https", "example.org", 314, null)
| ("https", "example.org", 420, null)
| ❌ | ❌ |
("https", "example.org", 314, "example.org")
| ("https", "example.org", 420, "example.org")
| ❌ | ✅ |
("https", "example.org", null, null)
| ("https", "example.org", null, "example.org")
| ✅ | ❌ |
("https", "example.org", null, "example.org")
| ("http", "example.org", null, "example.org")
| ❌ | ❌ |
domain [ = domain ]Returns the current domain used for security checks.
Can be set to a value that removes subdomains, to change the origin's domain to allow pages on other subdomains of the same
domain (if they do the same thing) to access each other. (Can't be set in sandboxed
iframes.)
To determine if a string hostSuffixString is a registrable domain suffix of or is equal to a host originalHost, run these steps:
If hostSuffixString is the empty string, then return false.
Let host be the result of parsing hostSuffixString.
If host is failure, then return false.
If host is not equal to originalHost, then run these substeps:
If host or originalHost is not a domain, then return false.
This is meant to exclude hosts that are an IPv4 address or an IPv6 address.
If host, prefixed by a U+002E FULL STOP (.), does not exactly match the end of originalHost, then return false.
If host matches a suffix in the Public Suffix List, or, if host, prefixed by a U+002E FULL STOP (.), matches the end of a suffix in the Public Suffix List, then return false. [PSL]
Suffixes must be compared after applying the host parser algorithm.
Return true.
The domain attribute's getter must run
these steps:
If this Document object does not have a browsing context, then return the empty string.
Let effectiveDomain be this Document's origin's effective domain.
If effectiveDomain is null, then return the empty string.
Return effectiveDomain, serialized.
The domain attribute's setter must run these
steps:
If this Document object has no browsing
context, then throw a "SecurityError"
DOMException.
If this Document object's active sandboxing flag set has its
sandboxed document.domain browsing context
flag set, then throw a "SecurityError"
DOMException.
Let effectiveDomain be this Document's origin's effective domain.
If effectiveDomain is null, then throw a
"SecurityError" DOMException.
If the given value is not
a registrable domain suffix of and is not equal to effectiveDomain, then throw
a "SecurityError" DOMException.
Set this Document object's origin's domain to the result of parsing the given value.
The document.domain attribute is used to
enable pages on different hosts of a domain to access each other's DOMs.
Do not use the document.domain
attribute when using shared hosting. If an untrusted third party is able to host an HTTP server at
the same IP address but on a different port, then the same-origin protection that normally
protects two different sites on the same host will fail, as the ports are ignored when comparing
origins after the document.domain attribute has been
used.
A sandboxing flag set is a set of zero or more of the following flags, which are used to restrict the abilities that potentially untrusted resources have:
This flag prevents content from navigating browsing contexts other than the sandboxed browsing context itself (or browsing contexts further nested inside it), auxiliary browsing contexts (which are protected by the sandboxed auxiliary navigation browsing context flag defined next), and the top-level browsing context (which is protected by the sandboxed top-level navigation without user activation browsing context flag and sandboxed top-level navigation with user activation browsing context flag defined below).
If the sandboxed auxiliary navigation browsing context flag is not set, then in certain cases the restrictions nonetheless allow popups (new top-level browsing contexts) to be opened. These browsing contexts always have one permitted sandboxed navigator, set when the browsing context is created, which allows the browsing context that created them to actually navigate them. (Otherwise, the sandboxed navigation browsing context flag would prevent them from being navigated even if they were opened.)
This flag prevents content from creating new auxiliary browsing
contexts, e.g. using the target attribute or
the window.open() method.
This flag prevents content from navigating their top-level browsing context and prevents content from closing their top-level browsing context. It is consulted only from algorithms that are not triggered by user activation.
When the sandboxed top-level navigation without user activation browsing context flag is not set, content can navigate its top-level browsing context, but other browsing contexts are still protected by the sandboxed navigation browsing context flag and possibly the sandboxed auxiliary navigation browsing context flag.
This flag prevents content from navigating their top-level browsing context and prevents content from closing their top-level browsing context. It is consulted only from algorithms that are triggered by user activation.
As with the sandboxed top-level navigation without user activation browsing context flag, this flag only affects the top-level browsing context; if it is not set, other browsing contexts might still be protected by other flags.
This flag prevents content from instantiating plugins, whether
using the embed element, the object element, the applet element, or through navigation of a nested browsing context, unless
those plugins can be secured.
This flag forces content into a unique origin, thus preventing it from accessing other content from the same origin.
This flag also prevents script from reading from or writing to the
document.cookie IDL attribute, and blocks access to
localStorage.
This flag blocks form submission.
This flag disables the Pointer Lock API. [POINTERLOCK]
This flag blocks script execution.
This flag blocks features that trigger automatically, such as automatically playing a video or automatically focusing a form control.
This flag prevents URL schemes that use storage areas from being able to access the origin's data.
document.domain
browsing context flagThis flag prevents content from using the
document.domain setter.
This flag prevents content from escaping the sandbox by ensuring that any auxiliary browsing context it creates inherits the content's active sandboxing flag set.
This flag prevents content from using any of the following features to produce modal dialogs:
This flag disables the ability to lock the screen orientation. [SCREENORIENTATION]
This flag disables the Presentation API. [PRESENTATION]
When the user agent is to parse a sandboxing directive, given a string input, a sandboxing flag set output, it must run the following steps:
Split input on ASCII whitespace, to obtain tokens.
Let output be empty.
Add the following flags to output:
The sandboxed auxiliary navigation browsing context flag, unless tokens contains the allow-popups keyword.
The sandboxed top-level navigation without user activation browsing context flag, unless
tokens contains the allow-top-navigation keyword.
The sandboxed top-level navigation with user activation browsing context flag, unless
tokens contains either the allow-top-navigation-by-user-activation
keyword or the allow-top-navigation keyword.
This means that if the allow-top-navigation is present, the allow-top-navigation-by-user-activation
keyword will have no effect. For this reason, specifying both is a document conformance error.
The sandboxed origin browsing context flag, unless the tokens contains the allow-same-origin
keyword.
The allow-same-origin keyword
is intended for two cases.
First, it can be used to allow content from the same site to be sandboxed to disable scripting, while still allowing access to the DOM of the sandboxed content.
Second, it can be used to embed content from a third-party site, sandboxed to prevent that site from opening pop-up windows, etc, without preventing the embedded page from communicating back to its originating site, using the database APIs to store data, etc.
The sandboxed forms browsing context flag, unless tokens contains the allow-forms keyword.
The sandboxed pointer lock browsing context flag, unless tokens contains the allow-pointer-lock
keyword.
The sandboxed scripts browsing context flag, unless tokens contains the allow-scripts keyword.
The sandboxed automatic features browsing context flag, unless tokens contains the allow-scripts keyword (defined above).
This flag is relaxed by the same keyword as scripts, because when scripts are enabled these features are trivially possible anyway, and it would be unfortunate to force authors to use script to do them when sandboxed rather than allowing them to use the declarative features.
The sandbox propagates to auxiliary browsing contexts flag, unless
tokens contains the allow-popups-to-escape-sandbox
keyword.
The sandboxed modals flag, unless tokens contains the allow-modals keyword.
The sandboxed orientation lock browsing context flag, unless
tokens contains the allow-orientation-lock
keyword.
The sandboxed presentation browsing context flag, unless tokens
contains the allow-presentation
keyword.
Every top-level browsing context has a popup sandboxing flag set, which is a sandboxing flag set. When a browsing context is created, its popup sandboxing flag set must be empty. It is populated by the rules for choosing a browsing context given a browsing context name.
Every browsing context that is a nested browsing context has an
iframe sandboxing flag set, which is a sandboxing flag set.
Which flags in a nested browsing context's iframe sandboxing flag
set are set at any particular time is determined by the iframe element's sandbox attribute.
Every Document has an active sandboxing flag set, which is a
sandboxing flag set. When the Document is created, its active
sandboxing flag set must be empty. It is populated by the navigation
algorithm.
Every resource that is obtained by the navigation algorithm has a forced sandboxing flag set, which is a sandboxing flag set. A resource by default has no flags set in its forced sandboxing flag set, but other specifications can define that certain flags are set.
In particular, the forced sandboxing flag set is used by Content Security Policy. [CSP]
To implement the sandboxing for a Document object document,
populate document's active sandboxing flag set with the union of the flags
that are present in the following sandboxing flag
sets:
If document's browsing context is a top-level browsing context, then: the flags set on the browsing context's popup sandboxing flag set.
If document's browsing context is a
nested browsing context, then: the flags set on the browsing context's
iframe sandboxing flag set.
If document's browsing context is a nested browsing context, then: the flags set on the browsing context's parent browsing context's active document's active sandboxing flag set.
The flags set on document's resource's forced sandboxing flag set, if it has one.
The sequence of Documents in a browsing context is its session
history. Each browsing context, including nested browsing contexts, has a distinct session history. A browsing
context's session history consists of a flat list of session history entries. Each session history entry consists, at a
minimum, of a URL, and each entry may in addition have a state object, a
title, a Document object, form data, a scroll restoration mode, a scroll
position, a browsing context name, and other information associated with it.
Each entry, when first created, has a Document. However, when a
Document is not active, it's possible for it to be
discarded to free resources. The URL and
other data in a session history entry is then used to bring a new
Document into being to take the place of the original, in case the user agent finds
itself having to reactivate that Document.
Titles associated with session history
entries need not have any relation with the current title of the
Document. The title of a session history entry is intended to explain
the state of the document at that point, so that the user can navigate the document's history.
URLs without associated state objects are added to the session history as the user (or script) navigates from page to page.
Each Document object in a browsing context's session
history is associated with a unique History object which must all model the
same underlying session history.
The history attribute of the Window
interface must return the object implementing the History interface for this
Window object's associated
Document.
A state object is an object representing a user interface state.
Pages can add state objects to the session history. These are then returned to the script when the user (or script) goes back in the history, thus enabling authors to use the "navigation" metaphor even in one-page applications.
State objects are intended to be used for two main purposes:
first, storing a preparsed description of the state in the URL so that in the simple
case an author doesn't have to do the parsing (though one would still need the parsing for
handling URLs passed around by users, so it's only a minor
optimization), and second, so that the author can store state that one wouldn't store in the URL
because it only applies to the current Document instance and it would have to be
reconstructed if a new Document were opened.
An example of the latter would be something like keeping track of the precise coordinate from
which a pop-up div was made to animate, so that if the user goes back, it can be
made to animate to the same location. Or alternatively, it could be used to keep a pointer into a
cache of data that would be fetched from the server based on the information in the
URL, so that when going back and forward, the information doesn't have to be fetched
again.
At any point, one of the entries in the session history is the current entry. This is the entry representing the active document of the browsing context. Which entry is the current entry is changed by the algorithms defined in this specification, e.g. during session history traversal.
The current entry is usually an entry for the URL of the Document. However, it can also be one
of the entries for state objects added to the history by that
document.
An entry with persisted user state is one that also has user-agent defined state. This specification does not specify what kind of state can be stored.
For example, some user agents might want to persist the scroll position, or the values of form controls.
User agents that persist the value of form controls are encouraged to also persist
their directionality (the value of the element's dir attribute).
This prevents values from being displayed incorrectly after a history traversal when the user had
originally entered the values with an explicit, non-default directionality.
An entry's scroll restoration mode indicates whether the user agent should restore the persisted scroll position (if any) when traversing to it. The scroll restoration mode may be one of the following:
auto"manual"If unspecified, the scroll restoration mode of a new entry must be set to
"auto".
Entries that consist of state objects share the same
Document as the entry for the page that was active when they were added.
Contiguous entries that differ just by their URLs' fragments also share the same Document.
All entries that share the same Document (and that are therefore
merely different states of one particular document) are contiguous by definition.
Each Document in a browsing context can also have a latest
entry. This is the entry for that Document to which the browsing
context's session history was most recently traversed. When a
Document is created, it initially has no latest entry.
User agents may discard the Document
objects of entries other than the current entry that are not referenced from any
script, reloading the pages afresh when the user or script navigates back to such pages. This
specification does not specify when user agents should discard Document objects and
when they should cache them.
Entries that have had their Document objects discarded must, for the purposes of
the algorithms given below, act as if they had not. When the user or script navigates back or
forwards to a page which has no in-memory DOM objects, any other entries that shared the same
Document object with it must share the new object as well.
History interfaceenum ScrollRestoration { "auto", "manual" };
interface History {
readonly attribute unsigned long length;
attribute ScrollRestoration scrollRestoration;
readonly attribute any state;
void go(optional long delta = 0);
void back();
void forward();
void pushState(any data, DOMString title, optional USVString? url = null);
void replaceState(any data, DOMString title, optional USVString? url = null);
};
history . lengthReturns the number of entries in the joint session history.
history . scrollRestoration [ = value ]Returns the scroll restoration mode of the current entry in the session history.
Can be set, to change the scroll restoration mode of the current entry in the session history.
history . stateReturns the current state object.
history . go( [ delta ] )Goes back or forward the specified number of steps in the joint session history.
A zero delta will reload the current page.
If the delta is out of range, does nothing.
history . back()Goes back one step in the joint session history.
If there is no previous page, does nothing.
history . forward()Goes forward one step in the joint session history.
If there is no next page, does nothing.
history . pushState(data, title [, url ] )Pushes the given data onto the session history, with the given title, and, if provided and not null, the given URL.
history . replaceState(data, title [, url ] )Updates the current entry in the session history to have the given data, title, and, if provided and not null, URL.
The joint session history of a top-level browsing context is the union
of all the session histories of all browsing contexts of all the fully active
Document objects that share that top-level browsing context, with all
the entries that are current entries in their respective session histories removed except for the current entry of
the joint session history.
The current entry of the joint session history is the entry that most recently became a current entry in its session history.
Entries in the joint session history are ordered chronologically by the time they were added to their respective session histories. Each entry has an index; the earliest entry has index 0, and the subsequent entries are numbered with consecutively increasing integers (1, 2, 3, etc).
Since each Document in a browsing context might have a
different event loop, the actual state of the joint session history can
be somewhat nebulous. For example, two sibling iframe elements could both traverse from one unique origin to another at the same time,
so their precise order might not be well-defined; similarly, since they might only find out about
each other later, they might disagree about the length of the joint session
history.
The length attribute of the
History interface, on getting, must return the number of entries in the
top-level browsing context's joint session history. If this
History object is associated with a Document that is not
fully active, getting must instead throw a "SecurityError"
DOMException.
The actual entries are not accessible from script.
The scrollRestoration attribute
of the History interface, on getting, must return the scroll restoration mode of the
current entry in the session history. On setting, the scroll restoration mode
of the current entry in the session history must be set to the new
value. If this History object is associated with a Document that is
not fully active, both getting and setting must instead throw a
"SecurityError" DOMException.
The state attribute of the
History interface, on getting, must return the last value it was set to by the user
agent. If this History object is associated with a Document that is
not fully active, getting must instead throw a
"SecurityError" DOMException. Initially, its value must be
null.
When the go(delta) method is
invoked, if delta is zero, the user agent must act as if the
location.reload() method was called instead. Otherwise,
the user agent must traverse the history by a delta whose value is
delta. If this History object is associated with a Document
that is not fully active, invoking must instead throw a
"SecurityError" DOMException.
When the back() method is invoked, the user
agent must traverse the history by a delta −1. If this History
object is associated with a Document that is not fully active,
invoking must instead throw a "SecurityError"
DOMException.
When the forward() method is invoked, the
user agent must traverse the history by a delta +1. If this History
object is associated with a Document that is not fully active,
invoking must instead throw a "SecurityError"
DOMException.
Each top-level browsing context has a session history traversal queue, initially empty, to which tasks can be added.
Each top-level browsing context, when created, must begin running the following algorithm, known as the session history event loop for that top-level browsing context, in parallel:
Wait until this top-level browsing context's session history traversal queue is not empty.
Pull the first task from this top-level browsing context's session history traversal queue, and execute it.
Return to the first step of this algorithm.
The session history event loop helps coordinate cross-browsing-context transitions of the joint session history: since each browsing context might, at any particular time, have a different event loop (this can happen if the user agent has more than one event loop per unit of related browsing contexts), transitions would otherwise have to involve cross-event-loop synchronization.
To traverse the history by a delta delta, the user agent must append a task to this top-level browsing context's session history traversal queue, the task consisting of running the following steps:
If the index of the current entry of the joint session history plus delta is less than zero or greater than or equal to the number of items in the joint session history, then abort these steps.
Let specified entry be the entry in the joint session history whose index is the sum of delta and the index of the current entry of the joint session history.
Let specified browsing context be the browsing context of the specified entry.
If the specified browsing context's active document's unload a document algorithm is currently running, abort these steps.
Queue a task that consists of running the following substeps. The relevant event loop is that of the specified browsing context's active document. The task source for the queued task is the history traversal task source.
If there is an ongoing attempt to navigate specified browsing context
that has not yet matured (i.e. it has not passed the
point of making its Document the active document), then cancel that
attempt to navigate the browsing context.
If the specified browsing context's active document is not
the same Document as the Document of the specified
entry, then run these substeps:
Prompt to unload the active document of the specified browsing context. If the user refused to allow the document to be unloaded, then abort these steps.
Unload the active document of the specified browsing context with the recycle parameter set to false.
Traverse the history of the specified browsing context to the specified entry.
When the user navigates through a browsing context, e.g. using a browser's back and forward buttons, the user agent must traverse the history by a delta equivalent to the action specified by the user.
The pushState(data, title, url) method adds a state object entry to
the history.
Support: historyChrome for Android 56+Chrome 5+UC Browser for Android (limited) 11+iOS Safari 5.0+Firefox 4+IE 10+Samsung Internet 4+Opera Mini NoneAndroid Browser 4.2+Safari 6+Edge 12+Opera 11.5+
Source: caniuse.com
The replaceState(data, title, url) method updates the state object,
title, and optionally the URL of the current entry in the history.
When either of these methods is invoked, the user agent must run the following steps:
Let document be the unique Document object this
History object is associated with.
If document is not fully active, throw a
"SecurityError" DOMException.
Optionally, abort these steps. (For example, the user agent might disallow calls to these methods that are invoked on a timer, or from event listeners that are not triggered in response to a clear user action, or that are invoked in rapid succession.)
Let targetRealm be this History object's relevant Realm.
Let cloned data be StructuredClone(data, targetRealm). Rethrow any exceptions.
If the third argument is not null, run these substeps:
History object.SecurityError" DOMException
and abort these steps.Let new URL be the resulting URL record.
SecurityError" DOMException and abort these steps.SecurityError" DOMException and
abort these steps. (This prevents sandboxed content from spoofing other pages on the same
origin.)If the third argument is null, then let new URL be the URL of the current entry.
If the method invoked was the pushState()
method:
Remove all the entries in the browsing context's session history after the current entry. If the current entry is the last entry in the session history, then no entries are removed.
This doesn't necessarily have to affect the user agent's user interface.
Remove any tasks queued by the history traversal
task source that are associated with any Document objects in the
top-level browsing context's document family.
If appropriate, update the current entry to reflect any state that the user agent wishes to persist. The entry is then said to be an entry with persisted user state.
Add a state object entry to the session history, after the current entry, with cloned data as the state object, the given title as the title, new URL as the URL of the entry, and the scroll restoration mode of the current entry in the session history as the scroll restoration mode.
Update the current entry to be this newly added entry.
Otherwise, if the method invoked was the replaceState() method:
Update the current entry in the session history so that cloned data is the entry's new state object, the given title is the new title, and new URL is the entry's new URL.
If the current entry in the session history represents a non-GET request (e.g. it was the result of a POST submission) then update it to instead represent a GET request.
Set document's URL to new URL.
Since this is neither a navigation of the
browsing context nor a history traversal,
it does not cause a hashchange event to be fired.
Set history.state to
StructuredClone(cloned data, targetRealm).
Set the current entry's Document object's latest
entry to the current entry.
The title is purely advisory. User agents might use the title in the user interface.
User agents may limit the number of state objects added to the session history per page. If a
page hits the UA-defined limit, user agents must remove the entry immediately after the first
entry for that Document object in the session history after having added the new
entry. (Thus the state history acts as a FIFO buffer for eviction, but as a LIFO buffer for
navigation.)
Consider a game where the user can navigate along a line, such that the user is always at some coordinate, and such that the user can bookmark the page corresponding to a particular coordinate, to return to it later.
A static page implementing the x=5 position in such a game could look like the following:
<!DOCTYPE HTML> <!-- this is https://example.com/line?x=5 --> <html lang="en"> <title>Line Game - 5</title> <p>You are at coordinate 5 on the line.</p> <p> <a href="?x=6">Advance to 6</a> or <a href="?x=4">retreat to 4</a>? </p>
The problem with such a system is that each time the user clicks, the whole page has to be reloaded. Here instead is another way of doing it, using script:
<!DOCTYPE HTML>
<!-- this starts off as https://example.com/line?x=5 -->
<html lang="en">
<title>Line Game - 5</title>
<p>You are at coordinate <span id="coord">5</span> on the line.</p>
<p>
<a href="?x=6" onclick="go(1); return false;">Advance to 6</a> or
<a href="?x=4" onclick="go(-1); return false;">retreat to 4</a>?
</p>
<script>
var currentPage = 5; // prefilled by server
function go(d) {
setupPage(currentPage + d);
history.pushState(currentPage, document.title, '?x=' + currentPage);
}
onpopstate = function(event) {
setupPage(event.state);
}
function setupPage(page) {
currentPage = page;
document.title = 'Line Game - ' + currentPage;
document.getElementById('coord').textContent = currentPage;
document.links[0].href = '?x=' + (currentPage+1);
document.links[0].textContent = 'Advance to ' + (currentPage+1);
document.links[1].href = '?x=' + (currentPage-1);
document.links[1].textContent = 'retreat to ' + (currentPage-1);
}
</script>
In systems without script, this still works like the previous example. However, users that do have script support can now navigate much faster, since there is no network access for the same experience. Furthermore, contrary to the experience the user would have with just a naïve script-based approach, bookmarking and navigating the session history still work.
In the example above, the data argument to the pushState() method is the same information as would be sent
to the server, but in a more convenient form, so that the script doesn't have to parse the URL
each time the user navigates.
Applications might not use the same title for a session history entry as the
value of the document's title element at that time. For example, here is a simple
page that shows a block in the title element. Clearly, when navigating backwards to
a previous state the user does not go back in time, and therefore it would be inappropriate to
put the time in the session history title.
<!DOCTYPE HTML>
<HTML LANG=EN>
<TITLE>Line</TITLE>
<SCRIPT>
setInterval(function () { document.title = 'Line - ' + new Date(); }, 1000);
var i = 1;
function inc() {
set(i+1);
history.pushState(i, 'Line - ' + i);
}
function set(newI) {
i = newI;
document.forms.F.I.value = newI;
}
</SCRIPT>
<BODY ONPOPSTATE="set(event.state)">
<FORM NAME=F>
State: <OUTPUT NAME=I>1</OUTPUT> <INPUT VALUE="Increment" TYPE=BUTTON ONCLICK="inc()">
</FORM>
Most applications want to use the same scroll restoration mode value for all of
their history entries. To achieve this they can set the scrollRestoration attribute as soon as possible
(e.g., in the first script element in the document's head element) to
ensure that any entry added to the history session gets the desired scroll restoration mode.
<head>
<script>
if ('scrollRestoration' in history)
history.scrollRestoration = 'manual';
</script>
</head>
This section is non-normative.
The History interface is not meant to place restrictions on how implementations
represent the session history to the user.
For example, session history could be implemented in a tree-like manner, with each page having
multiple "forward" pages. This specification doesn't define how the linear list of pages in the
history object are derived from the actual session history as
seen from the user's perspective.
Similarly, a page containing two iframes has a history object distinct from the iframes' history objects, despite the fact that typical Web browsers present the
user with just one "Back" button, with a session history that interleaves the navigation of the
two inner frames and the outer page.
Security: It is suggested that to avoid letting a page "hijack" the history
navigation facilities of a UA by abusing pushState(),
the UA provide the user with a way to jump back to the previous page (rather than just going back
to the previous state). For example, the back button could have a drop down showing just the pages
in the session history, and not showing any of the states. Similarly, an aural browser could have
two "back" commands, one that goes back to the previous state, and one that jumps straight back to
the previous page.
For both pushState() and replaceState(), user agents are encouraged to prevent
abuse of these APIs via too-frequent calls or over-large state objects. As detailed above, the
algorithm explicitly allows user agents to ignore any such calls when appropriate.
Location interfaceEach Window object is associated with a unique instance of a Location
object, allocated when the Window object is created.
The Location exotic object is defined through a mishmash of IDL,
invocation of JavaScript internal methods post-creation, and overridden JavaScript internal
methods. Coupled with its scary security policy, please take extra care while implementing
this excrescence.
To create a Location object, run these steps:
Let location be a new Location platform
object.
Perform ! location.[[DefineOwnProperty]]("valueOf", {
[[Value]]: %ObjProto_valueOf%,
[[Writable]]: false,
[[Enumerable]]: false,
[[Configurable]]: false }).
Perform ! location.[[DefineOwnProperty]](@@toPrimitive, { [[Value]]: undefined, [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }).
Set the value of the [[DefaultProperties]] internal slot of location to location.[[OwnPropertyKeys]]().
Return location.
The addition of valueOf and @@toPrimitive own
data properties, as well as the fact that all of Location's IDL attributes are marked
[Unforgeable], is required by legacy code that consulted the
Location interface, or stringified it, to determine the document URL, and then used it in a security-sensitive way.
In particular, the valueOf, @@toPrimitive, and [Unforgeable] stringifier mitigations ensure that code such as foo[location] = bar or location + "" cannot be
misdirected.
location [ = value ]location [ = value ]Returns a Location object with the current page's location.
Can be set, to navigate to another page.
The Document object's location attribute's getter must return this
Document object's relevant global
object's Location object, if this Document object is fully
active, and null otherwise.
The Window object's location
attribute's getter must return this Window object's Location object.
Location objects provide a representation of the URL of the active document of their
Document's browsing context, and allow the
current entry of the browsing context's session history to be changed,
by adding or replacing entries in the history object.
interface Location { // but see also additional creation steps and overridden internal methods
[Unforgeable] stringifier attribute USVString href;
[Unforgeable] readonly attribute USVString origin;
[Unforgeable] attribute USVString protocol;
[Unforgeable] attribute USVString host;
[Unforgeable] attribute USVString hostname;
[Unforgeable] attribute USVString port;
[Unforgeable] attribute USVString pathname;
[Unforgeable] attribute USVString search;
[Unforgeable] attribute USVString hash;
[Unforgeable] void assign(USVString url);
[Unforgeable] void replace(USVString url);
[Unforgeable] void reload();
[Unforgeable, SameObject] readonly attribute DOMStringList ancestorOrigins;
};
toString()hrefReturns the Location object's URL.
Can be set, to navigate to the given URL.
originReturns the Location object's URL's origin.
protocolReturns the Location object's URL's scheme.
Can be set, to navigate to the same URL with a changed scheme.
hostReturns the Location object's URL's host and port (if different from the default
port for the scheme).
Can be set, to navigate to the same URL with a changed host and port.
hostnameReturns the Location object's URL's host.
Can be set, to navigate to the same URL with a changed host.
portReturns the Location object's URL's port.
Can be set, to navigate to the same URL with a changed port.
pathnameReturns the Location object's URL's path.
Can be set, to navigate to the same URL with a changed path.
searchReturns the Location object's URL's query (includes leading "?" if non-empty).
Can be set, to navigate to the same URL with a changed query (ignores leading "?").
hashReturns the Location object's URL's fragment (includes leading "#" if non-empty).
Can be set, to navigate to the same URL with a changed fragment (ignores leading "#").
assign(url)Navigates to the given URL.
replace(url)Removes the current page from the session history and navigates to the given URL.
reload()Reloads the current page.
ancestorOriginsReturns a DOMStringList object listing the origins of the ancestor browsing contexts, from the parent browsing
context to the top-level browsing context.
A Location object has an associated relevant Document,
which is this Location object's associated Document object's browsing context's active document.
A Location object has an associated url,
which is this Location object's relevant Document's URL.
A Location object has an associated ancestor origins list. When a
Location object is created, its ancestor origins list must be set to a
DOMStringList object whose associated list is the list of strings that
the following steps would produce:
Let output be a new list of strings.
Let current be the browsing context
of the Document with which this Location object is associated.
Loop: If current has no parent browsing context, jump to the step labeled end.
Let current be current's parent browsing context.
Append the Unicode serialization of current's active document's origin to output.
Return to the step labeled loop.
End: Return output.
A Location object has an associated Location-object-setter
navigate algorithm, which given a url, runs these steps:
If any of the following conditions are met, let replacement flag be unset; otherwise, let it be set:
Location object's relevant Document has
completely loaded, orclick event's isTrusted
attribute is true, orclick event, whose isTrusted attribute is true, is being handled.Location-object navigate, given url and
replacement flag.
To Location-object navigate, given a url and
replacement flag, run these steps:
The source browsing context is the responsible browsing context specified by the incumbent settings object.
Navigate the browsing context to url, with the exceptions enabled flag set. Rethrow any exceptions.
If the replacement flag is set or the browsing context's
session history contains only one Document, and that was the
about:blank Document created when the browsing context
was created, then the navigation must be done with replacement enabled.
The href attribute's getter must run these
steps:
If this Location object's relevant Document's
origin is not same origin-domain with the entry settings
object's origin, then throw a
"SecurityError" DOMException.
Return this Location object's url,
serialized.
The href attribute's setter must run these steps:
Parse the given value relative to the entry
settings object. If that failed, throw a TypeError exception.
Location-object-setter navigate to the resulting URL
record.
The href attribute setter intentionally
has no security check.
The origin attribute's getter must run
these steps:
If this Location object's relevant Document's
origin is not same origin-domain with the entry settings
object's origin, then throw a
"SecurityError" DOMException.
Return the Unicode serialization
of this Location object's url's origin.
It returns the Unicode rather than the ASCII serialization for
compatibility with MessageEvent.
The protocol attribute's getter must run
these steps:
If this Location object's relevant Document's
origin is not same origin-domain with the entry settings
object's origin, then throw a
"SecurityError" DOMException.
Return this Location object's url's scheme,
followed by ":".
The protocol attribute's setter must run these
steps:
If this Location object's relevant Document's
origin is not same origin-domain with the entry settings
object's origin, then throw a
"SecurityError" DOMException.
Let possibleFailure be the result of basic URL
parsing the given value, followed by ":", with copyURL
as url and scheme start state as state override.
Because the URL parser ignores multiple consecutive colons, providing a value
of "https:" (or even "https::::") is the same as
providing a value of "https".
If possibleFailure is failure, then throw a
"SyntaxError" DOMException.
If copyURL's scheme is not an HTTP(S) scheme, then terminate these steps.
Location-object-setter navigate to copyURL.
The host attribute's getter must run these
steps:
If this Location object's relevant Document's
origin is not same origin-domain with the entry settings
object's origin, then throw a
"SecurityError" DOMException.
If url's host is null, return the empty string.
If url's port is null, return url's host, serialized.
Return url's host, serialized, followed by ":" and url's port, serialized.
The host attribute's setter must run these steps:
If this Location object's relevant Document's
origin is not same origin-domain with the entry settings
object's origin, then throw a
"SecurityError" DOMException.
If copyURL's cannot-be-a-base-URL flag is set, terminate these steps.
Basic URL parse the given value, with copyURL as url and host state as state override.
Location-object-setter navigate to copyURL.
The hostname attribute's getter must
run these steps:
If this Location object's relevant Document's
origin is not same origin-domain with the entry settings
object's origin, then throw a
"SecurityError" DOMException.
If this Location object's url's
host is null, return the empty string.
Return this Location object's url's host, serialized.
The hostname attribute's setter must run these
steps:
If this Location object's relevant Document's
origin is not same origin-domain with the entry settings
object's origin, then throw a
"SecurityError" DOMException.
If copyURL's cannot-be-a-base-URL flag is set, terminate these steps.
Basic URL parse the given value, with copyURL as url and hostname state as state override.
Location-object-setter navigate to copyURL.
The port attribute's getter must run these
steps:
If this Location object's relevant Document's
origin is not same origin-domain with the entry settings
object's origin, then throw a
"SecurityError" DOMException.
If this Location object's url's
port is null, return the empty string.
Return this Location object's url's port, serialized.
The port attribute's setter must run these steps:
If this Location object's relevant Document's
origin is not same origin-domain with the entry settings
object's origin, then throw a
"SecurityError" DOMException.
If copyURL cannot have a username/password/port, then return.
If the given value is the empty string, then set copyURL's port to null.
Otherwise, basic URL parse the given value, with copyURL as url and port state as state override.
Location-object-setter navigate to copyURL.
The pathname attribute's getter must
run these steps:
If this Location object's relevant Document's
origin is not same origin-domain with the entry settings
object's origin, then throw a
"SecurityError" DOMException.
If url's cannot-be-a-base-URL flag is set, return the first string in url's path.
If url's path is empty, then return the empty string.
Return "/", followed by the strings in url's path (including empty strings), separated from each other by
"/".
The pathname attribute's setter must run these
steps:
If this Location object's relevant Document's
origin is not same origin-domain with the entry settings
object's origin, then throw a
"SecurityError" DOMException.
If copyURL's cannot-be-a-base-URL flag is set, terminate these steps.
Set copyURL's path to the empty list.
Basic URL parse the given value, with copyURL as url and path start state as state override.
Location-object-setter navigate to copyURL.
The search attribute's getter must run
these steps:
If this Location object's relevant Document's
origin is not same origin-domain with the entry settings
object's origin, then throw a
"SecurityError" DOMException.
If this Location object's url's
query is either null or the empty string, return the
empty string.
The search attribute's setter must run these
steps:
If this Location object's relevant Document's
origin is not same origin-domain with the entry settings
object's origin, then throw a
"SecurityError" DOMException.
If the given value is the empty string, set copyURL's query to null.
Otherwise, run these substeps:
Let input be the given value with a single leading "?"
removed, if any.
Set copyURL's query to the empty string.
Basic URL parse input, with
copyURL as url and query state as state override,
and the relevant Document's document's character
encoding as encoding override.
Location-object-setter navigate to copyURL.
The hash attribute's getter must run these
steps:
If this Location object's relevant Document's
origin is not same origin-domain with the entry settings
object's origin, then throw a
"SecurityError" DOMException.
If this Location object's url's
fragment is either null or the empty string, return
the empty string.
Return "#", followed by this Location object's url's fragment.
The hash attribute's setter must run these steps:
If this Location object's relevant Document's
origin is not same origin-domain with the entry settings
object's origin, then throw a
"SecurityError" DOMException.
Let input be the given value with a single leading "#"
removed, if any.
Set copyURL's fragment to the empty string.
Basic URL parse input, with copyURL as url and fragment state as state override.
Location-object-setter navigate to copyURL.
Unlike the equivalent API for the a and area elements,
the hash attribute's setter does not special case the
empty string to remain compatible with deployed scripts.
When the assign(url)
method is invoked, the user agent must run the following steps:
If this Location object's relevant Document's
origin is not same origin-domain with the entry settings
object's origin, then throw a
"SecurityError" DOMException.
Parse url relative to the entry
settings object. If that failed, throw a "SyntaxError"
DOMException.
When the replace(url)
method is invoked, the user agent must run the following steps:
Parse url relative to the entry
settings object. If that failed, throw a "SyntaxError"
DOMException.
Location-object navigate to the resulting URL
record with the replacement flag set.
The replace() method intentionally has
no security check.
When the reload() method is invoked, the
user agent must run the appropriate steps from the following list:
Location object's relevant Document's
origin is not same origin-domain with the entry settings
object's originThrow a "SecurityError" DOMException.
resize event in response to the user resizing the browsing
contextRepaint the browsing context and abort these steps.
iframe srcdoc documentReprocess the iframe
attributes of the browsing context's browsing context
container.
Perform an overridden reload, with the browsing context being navigated as the responsible browsing context. Rethrow any exceptions.
Navigate the browsing context to
this Location object's relevant Document's URL to perform an entry update of the
browsing context's current entry, with the exceptions
enabled flag set. The source browsing context must be the
browsing context being navigated. This is a reload-triggered
navigation. Rethrow any exceptions.
When a user requests that the active document of a browsing context
be reloaded through a user interface element, the user agent should navigate the browsing context to the same resource as that
Document, to perform an entry update of the browsing
context's current entry. This is a reload-triggered navigation.
In the case of non-idempotent methods (e.g. HTTP POST), the user agent should prompt the user to
confirm the operation first, since otherwise transactions (e.g. purchases or database
modifications) could be repeated. User agents may allow the user to explicitly override any caches
when reloading. If browsing context's active document's reload
override flag is set, then the user agent may instead perform an overridden
reload rather than the navigation described in this paragraph (with the browsing
context being reloaded as the source browsing context).
The ancestorOrigins attribute's
getter must run these steps:
If this Location object's relevant Document's
origin is not same origin-domain with the entry settings
object's origin, then throw a
"SecurityError" DOMException.
Otherwise, return this Location object's ancestor origins list.
As explained earlier, the Location exotic object
requires additional logic beyond IDL for security purposes. The internal slot and internal methods
Location objects must implement are defined below.
Every Location object has a [[DefaultProperties]] internal slot
representing its own properties at time of its creation.
If IsPlatformObjectSameOrigin(this) is true, then return ! OrdinaryGetPrototypeOf(this).
Return null.
Return false.
Return true.
Return false.
If IsPlatformObjectSameOrigin(this) is true, then:
Let desc be OrdinaryGetOwnProperty(this, P).
If the value of the [[DefaultProperties]] internal slot of this contains P, then set desc.[[Configurable]] to true.
Return desc.
Let property be ! CrossOriginGetOwnPropertyHelper(this, P).
If property is not undefined, return property.
Throw a "SecurityError" DOMException.
If IsPlatformObjectSameOrigin(this) is true, then:
If the value of the [[DefaultProperties]] internal slot of this contains P, then return false.
Return ? OrdinaryDefineOwnProperty(this, P, Desc).
Throw a "SecurityError" DOMException.
If IsPlatformObjectSameOrigin(this) is true, then return ? OrdinaryGet(this, P, Receiver).
Return ? CrossOriginGet(this, P, Receiver).
If IsPlatformObjectSameOrigin(this) is true, then return ? OrdinarySet(this, P, Receiver).
Return ? CrossOriginSet(this, P, V, Receiver).
If IsPlatformObjectSameOrigin(this) is true, then return ? OrdinaryDelete(this, P).
Throw a "SecurityError" DOMException.
If IsPlatformObjectSameOrigin(this) is true, then return ! OrdinaryOwnPropertyKeys(this).
Return ! CrossOriginOwnPropertyKeys(this).
Certain actions cause the browsing context to navigate to a new resource. A user agent may provide various ways for the user to explicitly cause a browsing context to navigate, in addition to those defined in this specification.
For example, following a hyperlink,
form submission, and the window.open() and location.assign() methods can all cause a browsing context to
navigate.
A resource has a URL, but that might not be the only information necessary
to identify it. For example, a form submission that uses HTTP POST would also have the HTTP method
and payload. Similarly, an iframe srcdoc document needs to know the data it is to use.
Navigation always involves source browsing context, which is the browsing context which was responsible for starting the navigation.
To navigate a browsing context browsingContext to a resource resource, optionally with an exceptions enabled flag, the user agent must run these steps:
If resource is a URL, then set resource to a new request whose url is resource.
If the source browsing context is not allowed to navigate browsingContext, then:
If the exceptions enabled flag is set, then throw a
"SecurityError" DOMException.
Otherwise, the user agent may instead offer to open resource in a new top-level browsing context or in the top-level browsing context of the source browsing context, at the user's option, in which case the user agent must navigate that designated top-level browsing context to resource as if the user had requested it independently.
Doing so, however, can be dangerous, as it means that the user is overriding the author's explicit request to sandbox the content.
If there is a preexisting attempt to navigate browsingContext, and the source browsing context is the same as browsingContext, and that attempt is currently running the unload a document algorithm, then abort these steps without affecting the preexisting attempt to navigate browsingContext.
If the prompt to unload a document algorithm is being run for the active document of browsingContext, then abort these steps without affecting the prompt to unload a document algorithm.
Cancel any preexisting but not yet mature
attempt to navigate browsingContext, including canceling any instances of the fetch algorithm started by those attempts. If one of those attempts
has already created and initialized a new
Document object, abort that
Document also. (Navigation attempts that have matured already have session history entries, and are
therefore handled during the update the session history with the new page algorithm,
later.)
Prompt to unload the active document of browsingContext. If the user refused to allow the document to be unloaded, then abort these steps.
If this instance of the navigation algorithm gets canceled while this step is running, the prompt to unload a document algorithm must nonetheless be run to completion.
Abort the active document of browsingContext.
If browsingContext is a nested browsing context, then put it in the
delaying load events mode.
The user agent must take this nested browsing context out of the delaying
load events mode when this navigation algorithm later matures, or when it terminates (whether due to having
run all the steps, or being canceled, or being aborted), whichever happens first.
Let navigationType be "form-submission" if the navigation algorithm was invoked as a result of the form submission algorithm, and "other"
otherwise.
Return to whatever algorithm invoked the navigation steps and continue running these steps in parallel.
This is the step that attempts to obtain resource, if necessary. Jump to the first appropriate substep:
Run process a navigate response with null, resource, navigationType, the source browsing context, and browsingContext, and then abort these steps.
javascript"Queue a task to run these
"javascript: URL" steps, associated with the active document
of browsingContext:
Let result be undefined, and jump to the step labeled process result below if either of the following are true:
The source browsing context's active document's origin is not the same origin as browsingContext's active document's origin.
The Should navigation request of type from source in target be blocked by
Content Security Policy? algorithm returns "Blocked" when
executed upon resource, "other", the source
browsing context, and browsingContext. [CSP]
Let urlString be the result of running the URL serializer on resource's url.
Remove the leading "javascript:" string from
urlString.
Let script source be the result of applying the percent decode algorithm to urlString.
Replace script source with the result of applying the UTF-8 decode algorithm to script source.
Let address be the URL of the active document of browsingContext.
Let settings be the relevant settings object for the active document of browsingContext.
Let script be the result of creating a classic script given script source and settings.
Let result be the result of running the classic script script. If evaluation was unsuccessful, let result be undefined instead. (The result will also be undefined if scripting is disabled.)
Let response be null.
Process result: If Type(result) is not
String, then set response to a response whose status is 204.
Otherwise, set response a response
whose header list consists of `Content-Type`/`text/html` and `Referrer-Policy`/settings's referrer
policy, whose body is result,
and whose HTTPS state is
settings's HTTPS state.
The exact conversion between the JavaScript string result and the bytes that comprise a response body is not yet specified, pending further investigation into user agent behavior. See issue #1129.
When it comes time to set the document's address, use address as the override URL.
Run process a navigate response with resource, response, navigationType, the source browsing context, and browsingContext, and then abort these steps.
The task source for this task is the DOM manipulation task source.
So for example a javascript: URL in
an href attribute of an a element
would only be evaluated when the link was followed, while such a URL in the src attribute of an iframe element would be
evaluated in the context of the iframe's own nested browsing
context when the iframe is being set up; once evaluated, its return value
(if it was a string) would replace that browsing context's
Document, thus also changing the Window object of that
browsing context.
GET`, and there are
relevant application caches that are
identified by a URL with the same origin as the URL in question, and that have
this URL as one of their entries, excluding entries marked as foreign, and whose mode is fast, and the user agent is not in a mode where it
will avoid using application cachesFetch resource from the most appropriate application cache of those that match.
For example, imagine an HTML page with an associated application cache displaying an image and a form, where the image is also used by several other application caches. If the user right-clicks on the image and chooses "View Image", then the user agent could decide to show the image from any of those caches, but it is likely that the most useful cache for the user would be the one that was used for the aforementioned HTML page. On the other hand, if the user submits the form, and the form does a POST submission, then the user agent will not use an application cache at all; the submission will be made to the network.
This still needs to be integrated with the Fetch standard. [FETCH]
Run process a navigate fetch given resource, the source browsing context, and browsing context, and type.
javascript" nor a fetch
schemeRun process a navigate URL scheme given resource's url and browsingContext.
To process a navigate fetch, given a request request, browsing context sourceBrowsingContext, browsing context browsingContext, and string type, run these steps:
Let response be null.
Set request's client to
sourceBrowsingContext's active document's relevant settings
object, destination to "document", mode to "navigate", credentials
mode to "include", use-URL-credentials flag, redirect mode to "manual",
and target client id to
browsingContext's active document's relevant settings
object's id.
If browsingContext is a child browsing context and the browsing context container of browsingContext has a browsing context scope origin, then set request's origin to that browsing context scope origin.
Create a new environment reservedEnvironment, and set its id to a new unique opaque string, its creation URL to request's url, and its target browsing context to browsingContext.
The created environment's active service worker is set in the handle fetch algorithm during the fetch if its creation URL matches a service worker registration. [SW]
Set request's reserved client to reservedEnvironment.
If the Should navigation request of type from source in target be blocked by Content
Security Policy? algorithm returns "Blocked" when executed upon
request, navigationType, sourceBrowsingContext, and
browsingContext, then set response to a network error.
[CSP]
Otherwise:
Fetch request.
Wait for the task on the networking task source to process response and set response to the result.
Otherwise, if response has a location URL that is a URL whose scheme is "blob", "file", "filesystem", or "javascript", then set response to a network error.
Otherwise, if response has a location URL that is a URL whose scheme is a fetch scheme, then run process a navigate fetch with a new request whose url is response's location URL, sourceBrowsingContext, browsingContext, and type.
Otherwise, if response has a location URL that is a URL, run the process a navigate URL scheme given response's location URL and browsingContext.
Fallback in prefer-online mode: If response was not fetched from
an application cache, and was to be fetched using `GET`, and
there are relevant application caches that are
identified by a URL with the same origin as the URL in question, and that have this
URL as one of their entries, excluding entries marked as foreign, and whose mode is prefer-online, and the user didn't cancel
the navigation attempt during the earlier step, and response is either a network
error or its status is not an ok
status, then:
Let candidate be the response identified by the URL in question from the most appropriate application cache of those that match.
If candidate is not marked as foreign, then the user agent must discard the failed load and instead continue along these steps using candidate as response. The user agent may indicate to the user that the original page load failed, and that the page used was a previously cached response.
Fallback for fallback entries: If response was not fetched from
an application cache, and was to be fetched using `GET`, and
its URL matches the fallback namespace
of one or more relevant application caches, and
the most appropriate application cache of those
that match does not have an entry in its online
safelist that has the same origin as response's URL and that is a
prefix match for response's URL, and the user didn't cancel the
navigation attempt during the earlier step, and response is either a network error or
its status is not an ok status,
then:
Let candidate be the fallback response specified for the fallback namespace in question. If multiple application caches match, the user agent must use the fallback of the most appropriate application cache of those that match.
If candidate is not marked as foreign, then the user agent must discard the failed load and instead continue along these steps using candidate as response. The document's URL, if appropriate, will still be the originally requested URL, not the fallback URL, but the user agent may indicate to the user that the original page load failed, that the page used was a fallback response, and what the URL of the fallback response actually is.
Run process a navigate response given request, response, navigationType, the source browsing context, browsingContext, and reservedEnvironment.
To process a navigate response, given a request request, a response response, a string type, two browsing contexts source and browsingContext, and an optional environment reservedEnvironment, run these steps:
If any of the following are true, then display the inline
content with an appropriate error shown to the user, with the newly created
Document object's origin set to a new opaque origin, and abort these steps.
response is a network error.
TODO: Define X-Frame-Options
processing here [whatwg/html#1230].
The Should navigation response to navigation request of type from source in target
be blocked by Content Security Policy? algorithm returns "Blocked" when executed upon request, response,
type, source, and browsingContext. [CSP]
This is where the network errors defined and propagated by the WHATWG Fetch standard, such as DNS or TLS errors, end up being displayed to users. [FETCH]
If response's status is
204 or 205, then abort these steps.
If response has an `Content-Disposition` header specifying the attachment disposition type, then handle it as a download and abort
these steps.
Let type be the computed type of response.
If the user agent has been configured to process resources of the given type using some mechanism other than rendering the content in a browsing context, then skip this step. Otherwise, if the type is one of the following types, jump to the appropriate entry in the following list, and process response as described there:
text/cache-manifest"text/css"text/plain"text/vtt"multipart/x-mixed-replace"An explicitly supported XML type is one for which the user agent is configured to
use an external application to render the content (either a plugin rendering
directly in browsingContext, or a separate application), or one for which the user
agent has dedicated processing rules (e.g. a Web browser with a built-in Atom feed viewer would
be said to explicitly support the application/atom+xml MIME type), or one for which
the user agent has a dedicated handler (e.g. one registered using registerContentHandler()).
The term JSON MIME type is used to refer to the MIME
types application/json, text/json, and any MIME
type whose subtype ends with the five characters "+json".
An explicitly supported JSON type is one for which the user agent is configured to
use an external application to render the content (either a plugin rendering
directly in browsingContext, or a separate application), or one for which the user
agent has dedicated processing rules, or one for which the user agent has a dedicated handler
(e.g. one registered using registerContentHandler()).
Setting the document's address: If there is no
override URL, then any Document created by these steps must have its
URL set to the URL that was
originally to be fetched, ignoring any other data that was used to obtain the resource. However,
if there is an override URL, then any Document created by
these steps must have its URL set to that
URL instead.
An override URL is set when dereferencing a javascript: URL and when
performing an overridden reload.
Initializing a new Document object: when a
Document is created as part of the above steps, the user agent will be required to
additionally run the following algorithm after creating the new object:
Let window be null.
Let settingsObject be null.
If browsingContext's only entry in its session history is the
about:blank Document that was added when browsingContext
was created, and navigation is occurring
with replacement enabled, and that Document has the same
origin as the new Document, then set window to the
Window object of that Document, and set settingsObject to
window's relevant settings object.
Otherwise,
Call the JavaScript InitializeHostDefinedRealm() abstract operation with the following customizations:
For the global object, create a new Window object and set
window to it.
For the global this value, use browsingContext's
WindowProxy object.
Let realm execution context be the created JavaScript execution context.
Set up a browsing context environment settings object with realm execution context and reservedEnvironment, if present, and set settingsObject to the result.
Set window's associated
Document to the new Document.
Set browsingContext's WindowProxy object's
[[Window]] internal slot
value to window.
Set the Document's HTTPS
state to the HTTPS state of the response used to generate the document.
Set the Document's referrer
policy to the result of parsing the
`Referrer-Policy` header of the response used to generate the document. [REFERRERPOLICY]
Execute the Initialize a Document's CSP list
algorithm on the Document object and the response used to generate the document. [CSP]
If resource is a request, then set the document's referrer to the serialization of resource's referrer, if resource's referrer is a URL record, and the empty string otherwise.
Per the WHATWG Fetch standard a request's referrer will be either a URL record or
"no-referrer" at this point.
Implement the sandboxing for the Document.
Set the allow* flags for the Document.
Set settingsObject's execution ready flag.
If settingsObject's active service worker is not null, then:
If settingsObject is a secure context, then:
If browsingContext has an opener browsing context and request's client is a non-secure context, then disown browsingContext's opener.
Otherwise, set settingsObject's active service worker to null.
Otherwise, the document's type is such that the resource will not affect browsingContext, e.g., because the resource is to be handed to an external application or because it is an unknown type that will be processed as a download. Process the resource appropriately.
To process a navigate URL scheme, given a URL url and browsing context browsingContext, run these steps:
If url is to be handled using a mechanism that does not affect browsingContext, e.g., because url's scheme is handled externally, then proceed with that mechanism instead.
Otherwise, url is to be handled by displaying some sort of inline content, e.g., an error message because the specified scheme is not one of the supported protocols, or an inline prompt to allow the user to select a registered handler for the given scheme. Display the inline content.
In the case of a registered handler being used, navigate will be invoked with a new URL.
When a resource is handled by passing its URL or
data to an external software package separate from the user agent (e.g. handing a mailto: URL to a mail client, or a Word document to a word
processor), user agents should attempt to mitigate the risk that this is an attempt to exploit the
target software, e.g. by prompting the user to confirm that the source browsing
context's active document's origin is to be allowed to invoke the
specified software. In particular, if the navigate algorithm, when it was invoked,
was not triggered by user activation, the user agent should not invoke the external
software package without prior user confirmation.
For example, there could be a vulnerability in the target software's URL handler which a hostile page would attempt to exploit by tricking a user into clicking a link.
Some of the sections below, to which the above algorithm defers in certain cases, require the
user agent to update the session history with the new page. When a user agent is
required to do this, it must queue a task (associated with the Document
object of the current entry, not the new one) to run the following steps:
Unload the Document object of the
current entry, with the recycle parameter set to false.
If this instance of the navigation algorithm is canceled while this step is running the unload a document algorithm, then the unload a document algorithm must be allowed to run to completion, but this instance of the navigation algorithm must not run beyond this step. (In particular, for instance, the cancelation of this algorithm does not abort any event dispatch or script execution occurring as part of unloading the document or its descendants.)
Replace the Document of the entry being updated, and any other entries
that referenced the same document as that entry, with the new Document.
Traverse the history to the new entry.
Replace the current entry with a new entry representing the new resource
and its Document object, related state, and the default scroll restoration
mode of "auto".
Traverse the history to the new entry.
Remove all the entries in the browsing context's session history after the current entry. If the current entry is the last entry in the session history, then no entries are removed.
This doesn't necessarily have to affect the user agent's user interface.
Append a new entry at the end of the History object representing the new
resource and its Document object, related state, and the default scroll
restoration mode of "auto".
Traverse the history to the new entry. If the navigation was initiated with replacement enabled, then the traversal must itself be initiated with replacement enabled.
The navigation algorithm has now matured.
Fragment loop: Spin the event loop for a user-agent-defined amount of time, as desired by the user agent implementor. (This is intended to allow the user agent to optimize the user experience in the face of performance concerns.)
If the Document object has no parser, or its parser has stopped parsing, or the user agent has reason to believe the user is no longer
interested in scrolling to the fragment, then abort
these steps.
Scroll to the fragment given in the document's URL. If this fails to find an indicated part of the document, then return to the fragment loop step.
The task source for this task is the networking task source.
When an HTML document is to be loaded in a browsing context, the user agent must
queue a task to create a Document object, mark it as being an HTML document, set its content type to "text/html",
initialize the Document object, and finally create an HTML
parser and associate it with the Document. Each task that the networking task source places on the
task queue while fetching runs must then fill the parser's input byte
stream with the fetched bytes and cause the HTML parser to perform the
appropriate processing of the input stream.
The input byte stream converts bytes into characters for use in the tokenizer. This process relies, in part, on character encoding information found in the real Content-Type metadata of the resource; the computed type is not used for this purpose.
When no more bytes are available, the user agent must queue a task for the parser
to process the implied EOF character, which eventually causes a load event to be fired.
After creating the Document object, but before any script execution, certainly
before the parser stops, the user agent must update the
session history with the new page.
Application cache selection happens in the HTML parser.
The task source for the two tasks mentioned in this section must be the networking task source.
Spec bugs: 17976
When faced with displaying an XML file inline, user agents must follow the requirements defined
in the XML and Namespaces in XML recommendations, RFC 7303, DOM, and other relevant specifications
to create a Document object and a corresponding XML parser. [XML] [XMLNS] [RFC7303] [DOM]
At the time of writing, the XML specification community had not actually yet specified how XML and the DOM interact.
After the Document is created, the user agent must initialize the
Document object.
The actual HTTP headers and other metadata, not the headers as mutated or implied by the algorithms given in this specification, are the ones that must be used when determining the character encoding according to the rules given in the above specifications. Once the character encoding is established, the document's character encoding must be set to that character encoding.
If the document element, as parsed according to the XML specifications cited
above, is found to be an html element with an attribute manifest whose value is not the empty string, then, as soon as
the element is inserted into the document,
the user agent must parse the value of that attribute relative
to that element's node document, and if that is successful, must apply the URL serializer algorithm to the resulting URL
record with the exclude fragment flag set to obtain manifest URL, and
then run the application cache selection algorithm
with manifest URL as the manifest URL, passing in the newly-created
Document. Otherwise, if the attribute is absent, its value is the empty string, or
parsing its value fails, then as soon as the document element is inserted into the document, the user agent must run the application cache selection algorithm with no manifest, and
passing in the Document.
Because the processing of the manifest
attribute happens only once the document element is parsed, any URLs referenced by
processing instructions before the document element (such as <?xml-stylesheet?> PIs) will be fetched from the network and cannot be
cached.
User agents may examine the namespace of the root Element node of this
Document object to perform namespace-based dispatch to alternative processing tools,
e.g. determining that the content is actually a syndication feed and passing it to a feed handler.
If such processing is to take place, abort the steps in this section, and jump to the next step (labeled non-document content) in the
navigate steps above.
Otherwise, then, with the newly created Document, the user agent must update
the session history with the new page. User agents may do this before the complete document
has been parsed (thus achieving incremental rendering), and must do this before any scripts
are to be executed.
Error messages from the parse process (e.g. XML namespace well-formedness errors) may be
reported inline by mutating the Document.
When a plain text document is to be loaded in a browsing context, the user agent
must queue a task to create a Document object, mark it as being an HTML document, set its content type to the computed MIME type of the resource (type in the
navigate algorithm), initialize the Document object,
create an HTML parser, associate it with the Document, act as if the
tokenizer had emitted a start tag token with the tag name "pre" followed by a single U+000A LINE
FEED (LF) character, and switch the HTML parser's tokenizer to the PLAINTEXT
state. Each task that the networking task
source places on the task queue while fetching runs must then fill the
parser's input byte stream with the fetched bytes and cause the HTML
parser to perform the appropriate processing of the input stream.
The rules for how to convert the bytes of the plain text document into actual characters, and the rules for actually rendering the text to the user, are defined by the specifications for the computed MIME type of the resource (type in the navigate algorithm).
The document's character encoding must be set to the character encoding used to decode the document.
Upon creation of the Document object, the user agent must run the application cache selection algorithm with no manifest, and
passing in the newly-created Document.
When no more bytes are available, the user agent must queue a task for the parser
to process the implied EOF character, which eventually causes a load event to be fired.
After creating the Document object, but potentially before the page has finished
parsing, the user agent must update the session history with the new page.
User agents may add content to the head element of the Document,
e.g., linking to a style sheet, providing script, or giving the document a title.
In particular, if the user agent supports the Format=Flowed
feature of RFC 3676 then the user agent would need to apply extra styling to cause the text to
wrap correctly and to handle the quoting feature. This could be performed using, e.g., a CSS
extension.
The task source for the two tasks mentioned in this section must be the networking task source.
multipart/x-mixed-replace resourcesWhen a resource with the type multipart/x-mixed-replace is to be loaded in a
browsing context, the user agent must parse the resource using the rules for
multipart types. [RFC2046]
For each body part obtained from the resource, the user agent must run process a navigate
response using the new body part and the same browsing context, with
replacement enabled if a previous body part from the same resource resulted in a
Document object being created and initialized, and otherwise using the same setup as the navigate
attempt that caused this section to be invoked in the first place.
For the purposes of algorithms processing these body parts as if they were complete stand-alone resources, the user agent must act as if there were no more bytes for those resources whenever the boundary following the body part is reached.
Thus, load events (and for that matter unload events) do fire for each body part loaded.
When an image, video, or audio resource is to be loaded in a browsing context, the
user agent should create a Document object, mark it as being an HTML document, set its content
type to the computed MIME type of the
resource (type in the navigate algorithm), initialize the
Document object, append an html element to the
Document, append a head element and a body element to the
html element, append an element host element for the media, as described
below, to the body element, and set the appropriate attribute of the element
host element, as described below, to the address of the image, video, or audio
resource.
The element host element to create for the media is the element given in the table below in the second cell of the row whose first cell describes the media. The appropriate attribute to set is the one given by the third cell in that same row.
| Type of media | Element for the media | Appropriate attribute |
|---|---|---|
| Image | img
| src
|
| Video | video
| src
|
| Audio | audio
| src
|
Then, the user agent must act as if it had stopped parsing.
Upon creation of the Document object, the user agent must run the application cache selection algorithm with no manifest, and
passing in the newly-created Document.
After creating the Document object, but potentially before the page has finished
fully loading, the user agent must update the session history with the new page.
User agents may add content to the head element of the Document, or
attributes to the element host element, e.g., to link to a style sheet, to provide a
script, to give the document a title, or to make the media autoplay.
When a resource that requires an external resource to be rendered is to be loaded in a
browsing context, the user agent should create a Document object, mark
it as being an HTML document and mark it as being a
plugin document, set its content
type to the computed MIME type of the
resource (type in the navigate algorithm), initialize the
Document object, append an html element to the
Document, append a head element and a body element to the
html element, append an embed to the body element, and
set the src attribute of the embed element to
the address of the resource.
The term plugin document is used by
Content Security Policy as part of the mechanism that ensures iframes
can't be used to evade plugin-types directives. [CSP]
Then, the user agent must act as if it had stopped parsing.
Upon creation of the Document object, the user agent must run the application cache selection algorithm with no manifest, and
passing in the newly-created Document.
After creating the Document object, but potentially before the page has finished
fully loading, the user agent must update the session history with the new page.
User agents may add content to the head element of the Document, or
attributes to the embed element, e.g. to link to a style sheet or to give the
document a title.
When the user agent is to display a user agent page inline in a browsing context,
the user agent should create a Document object, mark it as being an HTML document, set its content type to "text/html",
initialize the Document object, and then either associate that
Document with a custom rendering that is not rendered using the normal
Document rendering rules, or mutate that Document until it represents
the content the user agent wants to render.
Once the page has been set up, the user agent must act as if it had stopped parsing.
Upon creation of the Document object, the user agent must run the application cache selection algorithm with no manifest,
passing in the newly-created Document.
After creating the Document object, but potentially before the page has been
completely set up, the user agent must update the session history with the new
page.
When a user agent is supposed to navigate to a fragment, then the user agent must run the following steps:
Remove all the entries in the browsing context's session history after the current entry. If the current entry is the last entry in the session history, then no entries are removed.
This doesn't necessarily have to affect the user agent's user interface.
Remove any tasks queued by the history traversal
task source that are associated with any Document objects in the
top-level browsing context's document family.
Append a new entry at the end of the History object representing the new
resource and its Document object, related state, and current entry's
scroll restoration mode. Its URL must be set to the address to which
the user agent was navigating. The title must be left
unset.
Traverse the history to the new entry, with the non-blocking events flag set. This will scroll to the fragment given in what is now the document's URL.
If the scrolling fails because the relevant ID has not yet been parsed, then the original navigation algorithm will take care of the scrolling instead, as the last few steps of its update the session history with the new page algorithm.
When the user agent is required to scroll to the fragment and the indicated part of the document, if any, is being rendered, the user agent must either change the scrolling position of the document using the following algorithm, or perform some other action such that the indicated part of the document is brought to the user's attention. If there is no indicated part, or if the indicated part is not being rendered, then the user agent must do nothing. The aforementioned algorithm is as follows:
If there is no indicated part of the
document, set the Document's target element to null.
If the indicated part of the document is the top of the document, then:
Set the Document's target element to null.
Scroll to the beginning of the document for the Document. [CSSOMVIEW]
Otherwise:
Let target be element that is the indicated part of the document.
Set the Document's target element to
target.
Use the scroll an element into view algorithm to scroll target into view, with the align to top flag set. [CSSOMVIEW]
Run the focusing steps for target, with the
Document's viewport as the fallback target.
Move the sequential focus navigation starting point to target.
The indicated part of the document is the one that the fragment, if any, identifies. The semantics of the fragment in terms of mapping it to a node is defined by the
specification that defines the MIME type used by the Document (for
example, the processing of fragments for XML MIME types is the responsibility of RFC7303). [RFC7303]
There is also a target element for each Document, which is used in
defining the :target pseudo-class and is updated by the
above algorithm. It is initially null.
For HTML documents (and HTML MIME types), the following processing model must be followed to determine what the indicated part of the document is.
Apply the URL parser algorithm to the URL, and let fragid be the fragment component of the resulting URL record.
If fragid is the empty string, then the indicated part of the document is the top of the document; stop the algorithm here.
Let fragid bytes be the result of percent-decoding fragid.
Let decoded fragid be the result of running UTF-8 decode without BOM or fail on fragid bytes. If decoded fragid is failure, jump to the step labeled no decoded fragid.
If there is an element in the document tree that has an ID exactly equal to decoded fragid, then the first such element in tree order is the indicated part of the document; stop the algorithm here.
No decoded fragid: If there is an a element in the document tree that has a name
attribute whose value is exactly equal to fragid (not decoded
fragid), then the first such element in tree order is the indicated part
of the document; stop the algorithm here.
If fragid is an ASCII case-insensitive match for the
string top, then the indicated part of the document is the top
of the document; stop the algorithm here.
Otherwise, there is no indicated part of the document.
The task source for the task mentioned in this section must be the DOM manipulation task source.
When a user agent is required to traverse the history to a session history entry entry, optionally with replacement enabled, and optionally with the non-blocking events flag set, the user agent must act as follows.
This algorithm is not just invoked when explicitly going back or forwards in the session history — it is also invoked in other situations, for example when navigating a browsing context, as part of updating the session history with the new page.
If entry no longer holds a Document object, then
navigate the browsing
context to entry's URL to perform an entry update of
entry, and abort these steps. The "navigate" algorithm reinvokes this
"traverse" algorithm to complete the traversal, at which point there is a
Document object and so this step gets skipped. The navigation must be done using
the same source browsing context as was used the first time entry was
created. (This can never happen with replacement enabled.)
If the resource was obtained using a non-idempotent action, for example a POST form submission, or if the resource is no longer available, for example because the computer is now offline and the page wasn't cached, navigating to it again might not be possible. In this case, the navigation will result in a different page than previously; for example, it might be an error message explaining the problem or offering to resubmit the form.
If the current entry's title was not set by the pushState() or replaceState() methods, then set its title to the value
returned by the document.title IDL attribute.
If appropriate, update the current entry in the browsing
context's Document object's History object to reflect any state
that the user agent wishes to persist. The entry is then said to be an entry with persisted
user state.
If entry has a different Document object than the current
entry, then run the following substeps:
Remove any tasks queued by the history traversal
task source that are associated with any Document objects in the
top-level browsing context's document family.
If the origin of entry's Document object is not the
same as the origin of the current
entry's Document object, then run the following subsubsteps:
The current browsing context name must be stored with all the entries in
the history that are associated with Document objects with the same
origin as the active document and that are contiguous with the
current entry.
If the browsing context is a top-level browsing context, but not an auxiliary browsing context, then set the browsing context's name to the empty string.
Make entry's Document object the
active document of the browsing context.
If entry has a browsing context name, then run the following subsubsteps:
Set the browsing context's browsing context name to entry's browsing context name.
Clear any browsing context names of all
entries in the history that are associated with Document objects with the
same origin as the new active document and that are contiguous with
entry.
If entry's Document object has any
form controls whose autofill field name is "off", invoke the reset algorithm of each of those elements.
If the current document readiness of entry's Document
object is "complete", then queue a task to run the
following subsubsteps:
If the Document's page showing flag is true, then abort this
task (i.e. don't fire the event below).
Set the Document's page showing flag to true.
Run any session history document visibility change steps for Document that
are defined by other applicable specifications.
This is specifically intended for use by the Page Visibility specification. [PAGEVIS]
Fire an event named pageshow at the Document object's
Window object, using PageTransitionEvent, with the persisted attribute initialized to true,
and legacy target override flag set.
If entry has a URL whose fragment differs from that of the
current entry's when compared in a case-sensitive manner, and the two
share the same Document object, then let hash changed be true, and let
old URL be the current entry's URL and new URL be
entry's URL. Otherwise, let hash changed be false.
If the traversal was initiated with replacement enabled, remove the entry immediately before the specified entry in the session history.
If entry is not an entry with persisted user state, but its URL's fragment is non-null, then scroll to the fragment.
Set the current entry to entry.
Let targetRealm be the current Realm Record.
If entry has a state object, then let state be StructuredClone(entry's state object, targetRealm). Otherwise, let state be null.
Set history.state to state.
Let state changed be true if entry's Document object
has a latest entry, and that entry is not entry; otherwise let it be
false.
Set entry's Document object's latest entry to
entry.
If the non-blocking events flag is not set, then run the following substeps immediately. Otherwise, the non-blocking events flag is set; queue a task to run the following substeps instead.
If state changed is true, then fire an
event named popstate at the Document
object's Window object, using PopStateEvent, with the bubbles attribute initialized to true and the state attribute initialized state.
If entry is an entry with persisted user state, then the user agent may restore persisted user state and update aspects of the document and its rendering.
If hash changed is true, then fire an
event named hashchange at the browsing
context's Window object, using HashChangeEvent, with the bubbles attribute initialized to true, the oldURL attribute initialized to old URL,
and the newURL attribute initialized to
new URL.
The task source for the tasks mentioned above is the DOM manipulation task source.
When the user agent is to restore persisted user state from a history entry, it must run the following steps immediately:
If the entry has a scroll restoration mode, let scrollRestoration
be that. Otherwise let scrollRestoration be "auto"
If scrollRestoration is "manual" the user agent should not restore the scroll
position for the Document or any of its scrollable regions, with the exception of
any nested browsing contexts whose scroll restoration is controlled by their own history entry's
scroll restoration mode, otherwise, it may do so.
Optionally, update other aspects of the document and its rendering, for instance values of form fields, that the user agent had previously recorded.
This can even include updating the dir attribute
of textarea elements or input elements whose type attribute is in either the Text state or the Search state, if the persisted state includes the
directionality of user input in such controls.
Not restoring the scroll position by user agent does not imply that the scroll position will be left at any particular value (e.g., (0,0)). The actual scroll position depends on the navigation type and the user agent's particular caching strategy. So web applications cannot assume any particular scroll position but rather are urged to set it to what they want it to be.
PopStateEvent interface[Constructor(DOMString type, optional PopStateEventInit eventInitDict)]
interface PopStateEvent : Event {
readonly attribute any state;
};
dictionary PopStateEventInit : EventInit {
any state = null;
};
stateReturns a copy of the information that was provided to pushState() or replaceState().
The state attribute must return the
value it was initialized to. It represents the context information for the event, or null, if the
state represented is the initial state of the Document.
HashChangeEvent interfaceSupport: hashchangeChrome for Android 56+Chrome 5+UC Browser for Android 11+iOS Safari 4.0+Firefox 3.6+IE 8+Samsung Internet 4+Opera Mini NoneAndroid Browser 2.2+Safari 5+Edge 12+Opera 10.6+
Source: caniuse.com
[Constructor(DOMString type, optional HashChangeEventInit eventInitDict)]
interface HashChangeEvent : Event {
readonly attribute USVString oldURL;
readonly attribute USVString newURL;
};
dictionary HashChangeEventInit : EventInit {
USVString oldURL = "";
USVString newURL = "";
};
oldURLReturns the URL of the session history entry that was previously current.
newURLReturns the URL of the session history entry that is now current.
The oldURL attribute must return
the value it was initialized to. It represents context information for the event, specifically the
URL of the session history entry that was traversed from.
The newURL attribute must return
the value it was initialized to. It represents context information for the event, specifically the
URL of the session history entry that was traversed to.
PageTransitionEvent interface[Constructor(DOMString type, optional PageTransitionEventInit eventInitDict)]
interface PageTransitionEvent : Event {
readonly attribute boolean persisted;
};
dictionary PageTransitionEventInit : EventInit {
boolean persisted = false;
};
persistedFor the pageshow event, returns false if the page is
newly being loaded (and the load event will fire). Otherwise,
returns true.
For the pagehide event, returns false if the page is
going away for the last time. Otherwise, returns true, meaning that (if nothing conspires to
make the page unsalvageable) the page might be reused if the user navigates back to this
page.
Things that can cause the page to be unsalvageable include:
document.open()
beforeunload events
unload events
iframes that are not salvageable
WebSocket objects
Document
The persisted attribute must
return the value it was initialized to. It represents the context information for the event.
A Document has a salvageable state, which must initially be
true, a fired unload flag, which must initially be false, and a page showing
flag, which must initially be false. The page showing flag is used to ensure that
scripts receive pageshow and pagehide events in a consistent manner (e.g. that they never
receive two pagehide events in a row without an intervening
pageshow, or vice versa).
Event loops have a termination nesting level counter, which must initially be zero.
When a user agent is to prompt to unload a document, it must run the following steps.
Increase the event loop's termination nesting level by one.
Increase the Document's ignore-opens-during-unload counter by
one.
Let event be the result of creating an event using
BeforeUnloadEvent.
Initialize event's type attribute to beforeunload and its cancelable attribute true.
Decrease the event loop's termination nesting level by one.
If any event listeners were triggered by the earlier dispatch step, then set the
Document's salvageable state to
false.
If the Document's active sandboxing flag set does not have its
sandboxed modals flag set, and the returnValue attribute of the event
object is not the empty string, or if the event was canceled, then the user agent may ask the
user to confirm that they wish to unload the document.
The message shown to the user is not customizable, but instead determined by
the user agent. In particular, the actual value of the returnValue attribute is ignored.
The user agent is encouraged to avoid asking the user for confirmation if it judges that doing so would be annoying, deceptive, or pointless. A simple heuristic might be that if the user has not interacted with the document, the user agent would not ask for confirmation before unloading it.
If the user agent asks the user for confirmation, it must pause while waiting for the user's response.
If the user did not confirm the page navigation, then the user agent refused to allow the document to be unloaded.
If this algorithm was invoked by another instance of the "prompt to unload a document" algorithm (i.e. through the steps below that invoke this algorithm for all descendant browsing contexts), then jump to the step labeled end.
Let descendants be the list of the descendant browsing
contexts of the Document.
If descendants is not an empty list, then for each browsing context b in descendants run the following substeps:
Prompt to unload the active document of the browsing context b. If the user refused to allow the document to be unloaded, then the user implicitly also refused to allow this document to be unloaded; jump to the step labeled end.
If the salvageable state of the active document of the browsing context b is false, then set the salvageable state of this document to false also.
End: Decrease the Document's ignore-opens-during-unload
counter by one.
When a user agent is to unload a document, it must run the following
steps. These steps are passed an argument, recycle, which is either true or false,
indicating whether the Document object is going to be re-used. (This is set by the
document.open() method.)
Increase the event loop's termination nesting level by one.
Increase the Document's ignore-opens-during-unload counter by
one.
If the Document's page showing flag is false, then jump to the
step labeled unload event below (i.e. skip firing the pagehide event and don't rerun the unloading document
visibility change steps).
Set the Document's page showing flag to false.
Fire an event named pagehide at the Document object's Window
object, using PageTransitionEvent, with the persisted attribute initialized to true if the
Document object's salvageable state is
true, and false otherwise, and legacy target override flag set.
Run any unloading document visibility change steps for Document that
are defined by other applicable specifications.
This is specifically intended for use by the Page Visibility specification. [PAGEVIS]
Unload event: If the Document's fired unload flag is
false, then fire an event named unload at the Document's object Window
object, with legacy target override flag set.
Decrease the event loop's termination nesting level by one.
If any event listeners were triggered by the earlier unload event step, then set
the Document object's salvageable state
to false and set the Document's fired unload flag to true.
Run any unloading document cleanup steps for Document that are
defined by this specification and other applicable specifications.
If this algorithm was invoked by another instance of the "unload a document" algorithm (i.e. by the steps below that invoke this algorithm for all descendant browsing contexts), then jump to the step labeled end.
Let descendants be the list of the descendant browsing
contexts of the Document.
If descendants is not an empty list, then for each browsing context b in descendants run the following substeps:
Unload the active document of the browsing context b with the recycle parameter set to false.
If the salvageable state of the active document of the browsing context b is false, then set the salvageable state of this document to false also.
If both the Document's salvageable state and recycle are
false, then the Document's browsing
context must discard the
Document.
End: Decrease the Document's ignore-opens-during-unload
counter by one.
This specification defines the following unloading document cleanup steps. Other specifications can define more.
For each WebSocket object webSocket whose relevant global object is equal to window,
make disappear webSocket.
If this affected any WebSocket objects, then set the Document's salvageable state to false.
If the Document's salvageable
state is false, run the following substeps:
For each EventSource object eventSource whose relevant global object is equal to window,
forcibly close
eventSource.
Empty window's list of active timers.
BeforeUnloadEvent interfaceinterface BeforeUnloadEvent : Event {
attribute DOMString returnValue;
};
There are no BeforeUnloadEvent-specific initialization methods.
The BeforeUnloadEvent interface is a legacy interface which allows prompting to unload the document to be controlled
not only by canceling the event, but by setting the returnValue attribute to a value besides the
empty string. Authors should use the preventDefault() method, or other means of canceling
events, instead of using returnValue.
The returnValue attribute
controls the process of prompting to unload the
document. When the event is created, the attribute must be set to
the empty string. On getting, it must return the last value it was set to. On setting, the
attribute must be set to the new value.
This attribute is a DOMString only for historical reasons.
Any value besides the empty string will be treated as a request to ask the user for
confirmation.
If a Document is aborted, the user agent must
run the following steps:
Abort the active
documents of every child browsing context. If this results in any of those
Document objects having their salvageable state set to false, then set this
Document's salvageable state to false
also.
Cancel any instances of the fetch algorithm in the
context of this Document, discarding any tasks
queued for them, and discarding any further data received from
the network for them. If this resulted in any instances of the fetch algorithm being canceled or any queued tasks or any network data getting
discarded, then set the Document's salvageable state to false.
If the Document has an active parser, then abort that parser and set the Document's salvageable state to false.
User agents may allow users to explicitly invoke the abort a
document algorithm for a Document. If the user does so, then, if that
Document is an active document, the user agent should queue a
task to fire an event named abort at that Document's Window object
before invoking the abort algorithm.
Support: offline-appsChrome for Android 56+Chrome 4+UC Browser for Android 11+iOS Safari 3.2+Firefox 3.5+IE 10+Samsung Internet 4+Opera Mini NoneAndroid Browser 2.1+Safari 4+Edge 12+Opera 10.6+
Source: caniuse.com
This feature is in the process of being removed from the Web platform. (This is a long process that takes many years.) Using any of the offline Web application features at this time is highly discouraged. Use service workers instead. [SW]
This section is non-normative.
In order to enable users to continue interacting with Web applications and documents even when their network connection is unavailable — for instance, because they are traveling outside of their ISP's coverage area — authors can provide a manifest which lists the files that are needed for the Web application to work offline and which causes the user's browser to keep a copy of the files for use offline.
To illustrate this, consider a simple clock applet consisting of an HTML page "clock1.html", a CSS style sheet "clock.css", and a
JavaScript script "clock.js".
Before adding the manifest, these three files might look like this:
<!-- clock1.html --> <!DOCTYPE HTML> <html> <head> <meta charset="utf-8"> <title>Clock</title> <script src="clock.js"></script> <link rel="stylesheet" href="clock.css"> </head> <body> <p>The time is: <output id="clock"></output></p> </body> </html>
/* clock.css */
output { font: 2em sans-serif; }
/* clock.js */
setInterval(function () {
document.getElementById('clock').value = new Date();
}, 1000);
If the user tries to open the "clock1.html" page while offline, though,
the user agent (unless it happens to have it still in the local cache) will fail with an
error.
The author can instead provide a manifest of the three files, say "clock.appcache":
CACHE MANIFEST clock2.html clock.css clock.js
With a small change to the HTML file, the manifest (served as text/cache-manifest)
is linked to the application:
<!-- clock2.html --> <!DOCTYPE HTML> <html manifest="clock.appcache"> <head> <meta charset="utf-8"> <title>Clock</title> <script src="clock.js"></script> <link rel="stylesheet" href="clock.css"> </head> <body> <p>The time is: <output id="clock"></output></p> </body> </html>
Now, if the user goes to the page, the browser will cache the files and make them available even when the user is offline.
Authors are encouraged to include the main page in the manifest also, but in practice the page that referenced the manifest is automatically cached even if it isn't explicitly mentioned.
With the exception of "no-store" directive, HTTP cache headers and restrictions on
caching pages served over TLS (encrypted, using https:) are
overridden by manifests. Thus, pages will not expire from an application cache before the user
agent has updated it, and even applications served over TLS can be made to work offline.
This section is non-normative.
The application cache feature works best if the application logic is separate from the
application and user data, with the logic (markup, scripts, style sheets, images, etc) listed in
the manifest and stored in the application cache, with a finite number of static HTML pages for
the application, and with the application and user data stored in Web Storage or a client-side
Indexed Database, updated dynamically using Web Sockets, XMLHttpRequest, server-sent
events, or some other similar mechanism.
This model results in a fast experience for the user: the application immediately loads, and fresh data is obtained as fast as the network will allow it (possibly while stale data shows).
Legacy applications, however, tend to be designed so that the user data and the logic are mixed together in the HTML, with each operation resulting in a new HTML page from the server.
For example, consider a news application. The typical architecture of such an application, when not using the application cache feature, is that the user fetches the main page, and the server returns a dynamically-generated page with the current headlines and the user interface logic mixed together.
A news application designed for the application cache feature, however, would instead have the
main page just consist of the logic, and would then have the main page fetch the data separately
from the server, e.g. using XMLHttpRequest.
The mixed-content model does not work well with the application cache feature: since the content is cached, it would result in the user always seeing the stale data from the previous time the cache was updated.
While there is no way to make the legacy model work as fast as the separated model, it
can at least be retrofitted for offline use using the prefer-online application cache mode. To do so, list all the static
resources used by the HTML page you want to have work offline in an application cache manifest, use the manifest attribute to select that manifest from the HTML file,
and then add the following line at the bottom of the manifest:
SETTINGS: prefer-online NETWORK: *
This causes the application cache to only be used for master entries when the user is offline, and causes the application cache to be used as an atomic HTTP cache (essentially pinning resources listed in the manifest), while allowing all resources not listed in the manifest to be accessed normally when the user is online.
This section is non-normative.
When the user visits a page that declares a manifest, the browser will try to update the cache. It does this by fetching a copy of the manifest and, if the manifest has changed since the user agent last saw it, redownloading all the resources it mentions and caching them anew.
As this is going on, a number of events get fired on the ApplicationCache object
to keep the script updated as to the state of the cache update, so that the user can be notified
appropriately. The events are as follows:
| Event name | Interface | Fired when... | Next events |
|---|---|---|---|
checking
| Event
| The user agent is checking for an update, or attempting to download the manifest for the first time. This is always the first event in the sequence. | noupdate, downloading, obsolete, error
|
noupdate
| Event
| The manifest hadn't changed. | Last event in sequence. |
downloading
| Event
| The user agent has found an update and is fetching it, or is downloading the resources listed by the manifest for the first time. | progress, error, cached, updateready
|
progress
| ProgressEvent
| The user agent is downloading resources listed by the manifest.
The event object's total attribute returns the total number of files to be downloaded.
The event object's loaded attribute returns the number of files processed so far.
| progress, error, cached, updateready
|
cached
| Event
| The resources listed in the manifest have been downloaded, and the application is now cached. | Last event in sequence. |
updateready
| Event
| The resources listed in the manifest have been newly redownloaded, and the script can use
swapCache() to switch to the new cache.
| Last event in sequence. |
obsolete
| Event
| The manifest was found to have become a 404 or 410 page, so the application cache is being deleted. | Last event in sequence. |
error
| Event
| The manifest was a 404 or 410 page, so the attempt to cache the application has been aborted. | Last event in sequence. |
| The manifest hadn't changed, but the page referencing the manifest failed to download properly. | |||
| A fatal error occurred while fetching the resources listed in the manifest. | |||
| The manifest changed while the update was being run. | The user agent will try fetching the files again momentarily. |
These events are cancelable; their default action is for the user agent to show download progress information. If the page shows its own update UI, canceling the events will prevent the user agent from showing redundant progress information.
An application cache is a set of cached resources consisting of:
One or more resources (including their out-of-band metadata, such as HTTP headers, if any), identified by URLs, each falling into one (or more) of the following categories:
These are documents that were added to the cache because a browsing
context was navigated to that document and the document
indicated that this was its cache, using the manifest
attribute.
This is the resource corresponding to the URL that was given in a master
entry's html element's manifest attribute.
The manifest is fetched and processed during the application cache download
process. All the master entries have the
same origin as the manifest.
These are the resources that were listed in the cache's manifest in an explicit section.
These are the resources that were listed in the cache's manifest in a fallback section.
Explicit entries and Fallback entries can be marked as foreign, which means that they have a manifest attribute but that it doesn't point at this cache's
manifest.
A URL in the list can be flagged with multiple different types, and thus an entry can end up being categorized as multiple entries. For example, an entry can be a manifest entry and an explicit entry at the same time, if the manifest is listed within the manifest.
Zero or more fallback namespaces, each of which is mapped to a fallback entry.
These are URLs used as prefix match patterns for resources that are to be fetched from the network if possible, or to be replaced by the corresponding fallback entry if not. Each namespace URL has the same origin as the manifest.
Zero or more URLs that form the online safelist namespaces.
These are used as prefix match patterns, and declare URLs for which the user agent will ignore the application cache, instead fetching them normally (i.e. from the network or local HTTP cache as appropriate).
An online safelist wildcard flag, which is either open or blocking.
The open state indicates that any URL not listed as cached is to be implicitly treated as being in the online safelist namespaces; the blocking state indicates that URLs not listed explicitly in the manifest are to be treated as unavailable.
A cache mode flag, which is either in the fast state or the prefer-online state.
Each application cache has a completeness flag, which is either complete or incomplete.
An application cache group is a group of application caches, identified by the absolute URL of a resource manifest which is used to populate the caches in the group.
An application cache is newer than another if it was created after the other (in other words, application caches in an application cache group have a chronological order).
Only the newest application cache in an application cache group can have its completeness flag set to incomplete; the others are always all complete.
Each application cache group has an update status, which is one of the following: idle, checking, downloading.
A relevant application cache is an application cache that is the newest in its group to be complete.
Each application cache group has a list of pending master entries. Each entry in this
list consists of a resource and a corresponding Document object. It is used during
the application cache download process to ensure that new master entries are cached
even if the application cache download process was already running for their
application cache group when they were loaded.
An application cache group can be marked as obsolete, meaning that it must be ignored when looking at what application cache groups exist.
A cache host is a Document object.
Each cache host has an associated ApplicationCache object.
Each cache host initially is not associated with an application cache, but can become associated with one early during the page load process, when steps in the parser and in the navigation sections cause cache selection to occur.
Multiple application caches in different application cache groups can contain the same resource, e.g. if the manifests all reference that resource. If the user agent is to select an application cache from a list of relevant application caches that contain a resource, the user agent must use the application cache that the user most likely wants to see the resource from, taking into account the following:
A URL matches a fallback namespace if there exists a relevant application cache whose manifest's URL has the same origin as the URL in question, and that has a fallback namespace that is a prefix match for the URL being examined. If multiple fallback namespaces match the same URL, the longest one is the one that matches. A URL looking for a fallback namespace can match more than one application cache at a time, but only matches one namespace in each cache.
If a manifest https://example.com/app1/manifest declares that https://example.com/resources/images is a fallback namespace, and the user
navigates to https://example.com:80/resources/images/cat.png, then the user
agent will decide that the application cache identified by https://example.com/app1/manifest contains a namespace with a match for that
URL.
This section is non-normative.
This example manifest requires two images and a style sheet to be cached and safelists a CGI script.
CACHE MANIFEST # the above line is required # this is a comment # there can be as many of these anywhere in the file # they are all ignored # comments can have spaces before them # but must be alone on the line # blank lines are ignored too # these are files that need to be cached they can either be listed # first, or a "CACHE:" header could be put before them, as is done # lower down. images/sound-icon.png images/background.png # note that each file has to be put on its own line # here is a file for the online safelist -- it isn't cached, and # references to this file will bypass the cache, always hitting the # network (or trying to, if the user is offline). NETWORK: comm.cgi # here is another set of files to cache, this time just the CSS file. CACHE: style/default.css
It could equally well be written as follows:
CACHE MANIFEST NETWORK: comm.cgi CACHE: style/default.css images/sound-icon.png images/background.png
Offline application cache manifests can use absolute paths or even absolute URLs:
CACHE MANIFEST /main/home /main/app.js /settings/home /settings/app.js https://img.example.com/logo.png https://img.example.com/check.png https://img.example.com/cross.png
The following manifest defines a catch-all error page that is displayed for any page on the site while the user is offline. It also specifies that the online safelist wildcard flag is open, meaning that accesses to resources on other sites will not be blocked. (Resources on the same site are already not blocked because of the catch-all fallback namespace.)
So long as all pages on the site reference this manifest, they will get cached locally as they are fetched, so that subsequent hits to the same page will load the page immediately from the cache. Until the manifest is changed, those pages will not be fetched from the server again. When the manifest changes, then all the files will be redownloaded.
Subresources, such as style sheets, images, etc, would only be cached using the regular HTTP caching semantics, however.
CACHE MANIFEST FALLBACK: / /offline.html NETWORK: *
Manifests must be served using the text/cache-manifest MIME type. All
resources served using the text/cache-manifest MIME type must follow the
syntax of application cache manifests, as described in this section.
An application cache manifest is a text file, whose text is encoded using UTF-8. Data in application cache manifests is line-based. Newlines must be represented by U+000A LINE FEED (LF) characters, U+000D CARRIAGE RETURN (CR) characters, or U+000D CARRIAGE RETURN (CR) U+000A LINE FEED (LF) pairs. [ENCODING]
This is a willful violation of RFC 2046, which requires all text/* types to only allow CRLF line breaks. This requirement, however, is
outdated; the use of CR, LF, and CRLF line breaks is commonly supported and indeed sometimes CRLF
is not supported by text editors. [RFC2046]
The first line of an application cache manifest must consist of the string "CACHE", a single U+0020 SPACE character, the string "MANIFEST", and either a U+0020 SPACE character, a U+0009 CHARACTER TABULATION (tab) character, a U+000A LINE FEED (LF) character, or a U+000D CARRIAGE RETURN (CR) character. The first line may optionally be preceded by a U+FEFF BYTE ORDER MARK (BOM) character. If any other text is found on the first line, it is ignored.
Subsequent lines, if any, must all be one of the following:
Blank lines must consist of zero or more U+0020 SPACE and U+0009 CHARACTER TABULATION (tab) characters only.
Comment lines must consist of zero or more U+0020 SPACE and U+0009 CHARACTER TABULATION (tab) characters, followed by a single U+0023 NUMBER SIGN character (#), followed by zero or more characters other than U+000A LINE FEED (LF) and U+000D CARRIAGE RETURN (CR) characters.
Comments need to be on a line on their own. If they were to be included on a line with a URL, the "#" would be mistaken for part of a fragment.
Section headers change the current section. There are four possible section headers:
CACHE:
FALLBACK:
NETWORK:
SETTINGS:
Section header lines must consist of zero or more U+0020 SPACE and U+0009 CHARACTER TABULATION (tab) characters, followed by one of the names above (including the U+003A COLON character (:)) followed by zero or more U+0020 SPACE and U+0009 CHARACTER TABULATION (tab) characters.
Ironically, by default, the current section is the explicit section.
The format that data lines must take depends on the current section.
When the current section is the explicit section, data lines must consist of zero or more U+0020 SPACE and U+0009 CHARACTER TABULATION (tab) characters, a valid URL string identifying a resource other than the manifest itself, and then zero or more U+0020 SPACE and U+0009 CHARACTER TABULATION (tab) characters.
When the current section is the fallback section, data lines must consist of zero or more U+0020 SPACE and U+0009 CHARACTER TABULATION (tab) characters, a valid URL string identifying a resource other than the manifest itself, one or more U+0020 SPACE and U+0009 CHARACTER TABULATION (tab) characters, another valid URL string identifying a resource other than the manifest itself, and then zero or more U+0020 SPACE and U+0009 CHARACTER TABULATION (tab) characters.
When the current section is the online safelist section, data lines must consist of zero or more U+0020 SPACE and U+0009 CHARACTER TABULATION (tab) characters, either a single U+002A ASTERISK character (*) or a valid URL string identifying a resource other than the manifest itself, and then zero or more U+0020 SPACE and U+0009 CHARACTER TABULATION (tab) characters.
When the current section is the settings section, data lines must consist of zero or more U+0020 SPACE and U+0009 CHARACTER TABULATION (tab) characters, a setting, and then zero or more U+0020 SPACE and U+0009 CHARACTER TABULATION (tab) characters.
Currently only one setting is defined:
prefer-online". It sets the cache mode to prefer-online. (The cache mode defaults to fast.)Within a settings section, each setting must occur no more than once.
Manifests may contain sections more than once. Sections may be empty.
URLs that are to be fallback pages associated with fallback namespaces, and those namespaces themselves, must be given in fallback sections, with the namespace being the first URL of the data line, and the corresponding fallback page being the second URL. All the other pages to be cached must be listed in explicit sections.
Fallback namespaces and fallback entries must have the same origin as the manifest itself. Fallback namespaces must also be in the same path as the manifest's URL.
A fallback namespace must not be listed more than once.
Namespaces that the user agent is to put into the online safelist must all be specified in online safelist sections. (This is needed for any URL that the page is intending to use to communicate back to the server.) To specify that all URLs are automatically safelisted in this way, a U+002A ASTERISK character (*) may be specified as one of the URLs.
Authors should not include namespaces in the online safelist for which another namespace in the online safelist is a prefix match.
Relative URLs must be given relative to the manifest's own URL. All URLs in the manifest must have the same scheme as the manifest itself (either explicitly or implicitly, through the use of relative URLs). [URL]
URLs in manifests must not have fragments (i.e. the U+0023 NUMBER SIGN character isn't allowed in URLs in manifests).
Fallback namespaces and namespaces in the online safelist are matched by prefix match.
When a user agent is to parse a manifest, it means that the user agent must run the following steps:
UTF-8 decode the byte stream corresponding with the manifest to be parsed.
The UTF-8 decode algorithm strips a leading BOM, if any.
Let base URL be the absolute URL representing the manifest.
Apply the URL parser to base URL, and let manifest path be the path component thus obtained.
Remove all the characters in manifest path after the last U+002F SOLIDUS character (/), if any. (The first character and the last character in manifest path after this step will both be slashes, the URL path separator character.)
Apply the URL parser steps to the base URL, so that the components from its URL record can be used by the subsequent steps of this algorithm.
Let explicit URLs be an initially empty list of absolute URLs for explicit entries.
Let fallback URLs be an initially empty mapping of fallback namespaces to absolute URLs for fallback entries.
Let online safelist namespaces be an initially empty list of absolute URLs for an online safelist.
Let online safelist wildcard flag be blocking.
Let cache mode flag be fast.
Let input be the decoded text of the manifest's byte stream.
Let position be a pointer into input, initially pointing at the first character.
If the characters starting from position are "CACHE", followed by a U+0020 SPACE character, followed by "MANIFEST", then advance position to the next character after those. Otherwise, this isn't a cache manifest; abort this algorithm with a failure while checking for the magic signature.
If the character at position is neither a U+0020 SPACE character, a U+0009 CHARACTER TABULATION (tab) character, U+000A LINE FEED (LF) character, nor a U+000D CARRIAGE RETURN (CR) character, then this isn't a cache manifest; abort this algorithm with a failure while checking for the magic signature.
This is a cache manifest. The algorithm cannot fail beyond this point (though bogus lines can get ignored).
Collect a sequence of code points that are not U+000A LINE FEED (LF) or U+000D CARRIAGE RETURN (CR) characters from input given position, and ignore those characters. (Extra text on the first line, after the signature, is ignored.)
Let mode be "explicit".
Start of line: If position is past the end of input, then jump to the last step. Otherwise, collect a sequence of code points that are U+000A LINE FEED (LF), U+000D CARRIAGE RETURN (CR), U+0020 SPACE, or U+0009 CHARACTER TABULATION (tab) characters from input given position.
Now, collect a sequence of code points that are not U+000A LINE FEED (LF) or U+000D CARRIAGE RETURN (CR) characters from input given position, and let the result be line.
Drop any trailing U+0020 SPACE and U+0009 CHARACTER TABULATION (tab) characters at the end of line.
If line is the empty string, then jump back to the step labeled start of line.
If the first character in line is a U+0023 NUMBER SIGN character (#), then jump back to the step labeled start of line.
If line equals "CACHE:" (the word "CACHE" followed by a U+003A COLON character (:)), then set mode to "explicit" and jump back to the step labeled start of line.
If line equals "FALLBACK:" (the word "FALLBACK" followed by a U+003A COLON character (:)), then set mode to "fallback" and jump back to the step labeled start of line.
If line equals "NETWORK:" (the word "NETWORK" followed by a U+003A COLON character (:)), then set mode to "online safelist" and jump back to the step labeled start of line.
If line equals "SETTINGS:" (the word "SETTINGS" followed by a U+003A COLON character (:)), then set mode to "settings" and jump back to the step labeled start of line.
If line ends with a U+003A COLON character (:), then set mode to "unknown" and jump back to the step labeled start of line.
This is either a data line or it is syntactically incorrect.
Let position be a pointer into line, initially pointing at the start of the string.
Let tokens be a list of strings, initially empty.
While position doesn't point past the end of line:
Let current token be an empty string.
While position doesn't point past the end of line and the character at position is neither a U+0020 SPACE nor a U+0009 CHARACTER TABULATION (tab) character, add the character at position to current token and advance position to the next character in input.
Add current token to the tokens list.
While position doesn't point past the end of line and the character at position is either a U+0020 SPACE or a U+0009 CHARACTER TABULATION (tab) character, advance position to the next character in input.
Process tokens as follows:
Let urlRecord be the result of parsing the first item in tokens with base URL; ignore the rest.
If urlRecord is failure, then jump back to the step labeled start of line.
If urlRecord has a different scheme component than base URL (the manifest's URL), then jump back to the step labeled start of line.
Let new URL be the result of applying the URL serializer algorithm to urlRecord, with the exclude fragment flag set.
Add new URL to the explicit URLs.
Let part one be the first token in tokens, and let part two be the second token in tokens.
Let urlRecordOne be the result of parsing part one with base URL.
Let urlRecordTwo be the result of parsing part two with base URL.
If either urlRecordOne or urlRecordTwo are failure, then jump back to the step labeled start of line.
If the origin of either urlRecordOne or urlRecordTwo is not same origin with the manifest's URL origin, then jump back to the step labeled start of line.
Let part one path be the path component of urlRecordOne.
If manifest path is not a prefix match for part one path, then jump back to the step labeled start of line.
Let part one be the result of applying the URL serializer algorithm to urlRecordOne, with the exclude fragment flag set.
Let part two be the result of applying the URL serializer algorithm to urlRecordTwo, with the exclude fragment flag set.
If part one is already in the fallback URLs mapping as a fallback namespace, then jump back to the step labeled start of line.
Otherwise, add part one to the fallback URLs mapping as a fallback namespace, mapped to part two as the fallback entry.
If the first item in tokens is a U+002A ASTERISK character (*), then set online safelist wildcard flag to open and jump back to the step labeled start of line.
Otherwise, let urlRecord be the result of parsing the first item in tokens with base URL.
If urlRecord is failure, then jump back to the step labeled start of line.
If urlRecord has a different scheme component than base URL (the manifest's URL), then jump back to the step labeled start of line.
Let new URL be the result of applying the URL serializer algorithm to urlRecord, with the exclude fragment flag set.
Add new URL to the online safelist namespaces.
If tokens contains a single token, and that token is a
case-sensitive match for the string "prefer-online", then
set cache mode flag to prefer-online and jump back to the
step labeled start of line.
Otherwise, the line is an unsupported setting: do nothing; the line is ignored.
Do nothing. The line is ignored.
Jump back to the step labeled start of line. (That step jumps to the next, and last, step when the end of the file is reached.)
Return the explicit URLs list, the fallback URLs mapping, the online safelist namespaces, the online safelist wildcard flag, and the cache mode flag.
The resource that declares the manifest (with the manifest attribute) will always get taken from the cache,
whether it is listed in the cache or not, even if it is listed in an online safelist namespace.
If a resource is listed in the explicit section or as a fallback entry in the fallback section, the resource will always be taken from the cache, regardless of any other matching entries in the fallback namespaces or online safelist namespaces.
When a fallback namespace and an online safelist namespace overlap, the online safelist namespace has priority.
The online safelist wildcard flag is applied last, only for URLs that match neither the online safelist namespace nor the fallback namespace and that are not listed in the explicit section.
When the user agent is required (by other parts of this specification) to start the application cache download process for an absolute URL purported to identify a manifest, or for an application cache group, potentially given a particular cache host, and potentially given a master resource, the user agent must run the steps below. These steps are always run in parallel with the event loop tasks.
Some of these steps have requirements that only apply if the user agent shows caching
progress. Support for this is optional. Caching progress UI could consist of a progress bar
or message panel in the user agent's interface, or an overlay, or something else. Certain events
fired during the application cache download process allow the script to override the
display of such an interface. (Such events are delayed until after the load event has fired.)
The goal of this is to allow Web applications to provide more
seamless update mechanisms, hiding from the user the mechanics of the application cache mechanism.
User agents may display user interfaces independent of this, but are encouraged to not show
prominent update progress notifications for applications that cancel the relevant events.
The application cache download process steps are as follows:
Optionally, wait until the permission to start the application cache download process has been obtained from the user and until the user agent is confident that the network is available. This could include doing nothing until the user explicitly opts-in to caching the site, or could involve prompting the user for permission. The algorithm might never get past this point. (This step is particularly intended to be used by user agents running on severely space-constrained devices or in highly privacy-sensitive environments).
Atomically, so as to avoid race conditions, perform the following substeps:
Pick the appropriate substeps:
Let manifest URL be that absolute URL.
If there is no application cache group identified by manifest URL, then create a new application cache group identified by manifest URL. Initially, it has no application caches. One will be created later in this algorithm.
Let manifest URL be the absolute URL of the manifest used to identify the application cache group to be updated.
If that application cache group is obsolete, then abort this instance of the application cache download process. This can happen if another instance of this algorithm found the manifest to be 404 or 410 while this algorithm was waiting in the first step above.
Let cache group be the application cache group identified by manifest URL.
If these steps were invoked with a master
resource, then add the resource, along with the resource's Document, to cache group's list of pending
master entries.
If these steps were invoked with a cache host, and the status of cache group is checking or downloading, then queue a post-load task to run these steps:
Let showProgress be the result of firing
an event named checking at the
ApplicationCache singleton of that cache host, with the cancelable attribute initialized to true.
If showProgress is true and the user agent shows caching progress, then display some sort of user interface indicating to the user that the user agent is checking to see if it can download the application.
If these steps were invoked with a cache host, and the status of cache group is downloading, then also queue a post-load task to run these steps:
Let showProgress be the result of firing
an event named downloading at the
ApplicationCache singleton of that cache host, with the cancelable attribute initialized to true.
If showProgress is true and the user agent shows caching progress, then display some sort of user interface indicating to the user the application is being downloaded.
If the status of the cache group is either checking or downloading, then abort this instance of the application cache download process, as an update is already in progress.
Set the status of cache group to checking.
For each cache host associated with an application cache in cache group, queue a post-load task run these steps:
Let showProgress be the result of firing
an event named checking at the
ApplicationCache singleton of the cache host, with the cancelable attribute initialized to true.
If showProgress is true and the user agent shows caching progress, then display some sort of user interface indicating to the user that the user agent is checking for the availability of updates.
The remainder of the steps run in parallel.
If cache group already has an application cache in it, then this is an upgrade attempt. Otherwise, this is a cache attempt.
If this is a cache attempt, then this algorithm was invoked with a cache host; queue a post-load task to run these steps:
Let showProgress be the result of firing an
event named checking at the
ApplicationCache singleton of that cache host, with the cancelable attribute initialized to true.
If showProgress is true and the user agent shows caching progress, then display some sort of user interface indicating to the user that the user agent is checking for the availability of updates.
Let request be a new request whose
url is manifest URL, client is null, destination is the empty string, referrer is "no-referrer",
synchronous flag is set, credentials
mode is "include", and whose use-URL-credentials
flag is set.
Fetching the manifest: Let manifest be the result of fetching request. HTTP caching semantics should be honored for this request.
Parse manifest's body according to the rules for parsing manifests, obtaining a list of explicit entries, fallback entries and the fallback namespaces that map to them, entries for the online safelist, and values for the online safelist wildcard flag and the cache mode flag.
The MIME type of the resource is ignored — it is assumed to
be text/cache-manifest. In the future, if new manifest formats are supported, the
different types will probably be distinguished on the basis of the file signatures (for the
current format, that is the "CACHE MANIFEST" string at the top of the
file).
If fetching the manifest fails due to a 404 or 410 response status, then run these substeps:
Mark cache group as obsolete. This cache group no
longer exists for any purpose other than the processing of Document objects
already associated with an application cache in the cache
group.
Let task list be an empty list of tasks.
For each cache host associated with an application cache in cache group, create a task to run these steps and append it to task list:
Let showProgress be the result of firing
an event named obsolete at the
ApplicationCache singleton of the cache host, with the cancelable attribute initialized to true.
If showProgress is true and the user agent shows caching progress, then display some sort of user interface indicating to the user that the application is no longer available for offline use.
For each entry in cache group's list of pending master entries, create a task to run these steps and append it to task list:
Let showProgress be the result of firing
an event named error (not obsolete!) at the ApplicationCache
singleton of the Document for this entry, if there still is one, with the cancelable attribute initialized to true.
If showProgress is true and the user agent shows caching progress, then display some sort of user interface indicating to the user that the user agent failed to save the application for offline use.
If cache group has an application cache whose completeness flag is incomplete, then discard that application cache.
If appropriate, remove any user interface indicating that an update for this cache is in progress.
Let the status of cache group be idle.
For each task in task list, queue that task as a post-load task.
Abort the application cache download process.
Otherwise, if fetching the manifest fails in some other way (e.g. the server returns another 4xx or 5xx response, or there is a DNS error, or the connection times out, or the user cancels the download, or the parser for manifests fails when checking the magic signature), or if the server returned a redirect, then run the cache failure steps. [HTTP]
If this is an upgrade attempt and the newly
downloaded manifest is byte-for-byte identical to the manifest found in the
newest application cache in cache
group, or the response status is 304, then run these substeps:
Let cache be the newest application cache in cache group.
Let task list be an empty list of tasks.
For each entry in cache group's list of pending master entries, wait for the resource for this entry to have either completely downloaded or failed.
If the download failed (e.g. the server returns a 4xx or 5xx response, or there is a DNS error, the connection times out, or the user cancels the download), or if the resource is labeled with the "no-store" cache directive, then create a task to run these steps and append it to task list:
Let showProgress be the result of firing
an event named error at the
ApplicationCache singleton of the Document for this entry, if there
still is one, with the cancelable attribute
initialized to true.
If showProgress is true and the user agent shows caching progress, then display some sort of user interface indicating to the user that the user agent failed to save the application for offline use.
Otherwise, associate the Document for this entry with cache; store the resource for this entry in cache, if it
isn't already there, and categorize its entry as a master entry. If applying the URL parser
algorithm to the resource's URL results in a URL record that has a
non-null fragment component, the URL
used for the entry in cache must instead be the absolute URL
obtained from applying the URL serializer
algorithm to the URL record with the exclude fragment flag set
(application caches never include fragments).
For each cache host associated with an application cache in cache group, create a task to run these steps and append it to task list:
Let showProgress be the result of firing
an event named noupdate at the
ApplicationCache singleton of the cache host, with the cancelable attribute initialized to true.
If showProgress is true and the user agent shows caching progress, then display some sort of user interface indicating to the user that the application is up to date.
Empty cache group's list of pending master entries.
If appropriate, remove any user interface indicating that an update for this cache is in progress.
Let the status of cache group be idle.
For each task in task list, queue that task as a post-load task.
Abort the application cache download process.
Let new cache be a newly created application cache in cache group. Set its completeness flag to incomplete.
For each entry in cache group's list of pending master entries, associate the
Document for this entry with new cache.
Set the status of cache group to downloading.
For each cache host associated with an application cache in cache group, queue a post-load task to run these steps:
Let showProgress be the result of firing an
event named downloading at the
ApplicationCache singleton of the cache host, with the cancelable attribute initialized to true.
If showProgress is true and the user agent shows caching progress, then display some sort of user interface indicating to the user that a new version is being downloaded.
Let file list be an empty list of URLs with flags.
Add all the URLs in the list of explicit entries obtained by parsing manifest to file list, each flagged with "explicit entry".
Add all the URLs in the list of fallback entries obtained by parsing manifest to file list, each flagged with "fallback entry".
If this is an upgrade attempt, then add all the URLs of master entries in the newest application cache in cache group whose completeness flag is complete to file list, each flagged with "master entry".
If any URL is in file list more than once, then merge the entries into one entry for that URL, that entry having all the flags that the original entries had.
For each URL in file list, run the following steps. These steps may be
run in parallel for two or more of the URLs at a time. If, while running these steps, the
ApplicationCache object's abort() method
sends a signal to this instance of the application
cache download process algorithm, then run the cache failure steps
instead.
If the resource URL being processed was flagged as neither an "explicit entry" nor or a "fallback entry", then the user agent may skip this URL.
This is intended to allow user agents to expire resources not listed in the manifest from the cache. Generally, implementors are urged to use an approach that expires lesser-used resources first.
For each cache host associated with an application cache in cache group, queue a progress post-load task to run these steps:
Let showProgress be the result of firing
an event named progress at the
ApplicationCache singleton of the cache host, using
ProgressEvent, with the cancelable
attribute initialized to true, the lengthComputable attribute initialized to
true, the total attribute initialized to the
number of files in file list, and the loaded attribute initialized to the number of files
in file list that have been either downloaded or skipped so far. [XHR]
If showProgress is true and the user agent shows caching progress, then display some sort of user interface indicating to the user that a file is being downloaded in preparation for updating the application.
Let request be a new request whose
url is URL, client is null, destination is the empty string,
origin is
manifest URL's origin, referrer is "no-referrer",
synchronous flag is set, credentials mode is "include", use-URL-credentials flag is set, and redirect mode is "manual".
Fetch request. If this is an upgrade attempt, then use the newest application cache in cache group as an HTTP cache, and honor HTTP caching semantics (such as expiration, ETags, and so forth) with respect to that cache. User agents may also have other caches in place that are also honored.
If the previous step fails (e.g. the server returns a 4xx or 5xx response, or there is a DNS error, or the connection times out, or the user cancels the download), or if the server returned a redirect, or if the resource is labeled with the "no-store" cache directive, then run the first appropriate step from the following list: [HTTP]
If these steps are being run in parallel for any other URLs in file list, then abort these steps for those other URLs. Run the cache failure steps.
Redirects are fatal because they are either indicative of a network problem (e.g. a captive portal); or would allow resources to be added to the cache under URLs that differ from any URL that the networking model will allow access to, leaving orphan entries; or would allow resources to be stored under URLs different than their true URLs. All of these situations are bad.
Skip this resource. It is dropped from the cache.
Copy the resource and its metadata from the newest application cache in cache group whose completeness flag is complete, and act as if that was the fetched resource, ignoring the resource obtained from the network.
User agents may warn the user of these errors as an aid to development.
These rules make errors for resources listed in the manifest fatal, while making it possible for other resources to be removed from caches when they are removed from the server, without errors, and making non-manifest resources survive server-side errors.
Except for the "no-store" directive, HTTP caching rules that would cause a file to be expired or otherwise not cached are ignored for the purposes of the application cache download process.
Otherwise, the fetching succeeded. Store the resource in the new cache.
If the user agent is not able to store the resource (e.g. because of quota restrictions), the user agent may prompt the user or try to resolve the problem in some other manner (e.g. automatically pruning content in other caches). If the problem cannot be resolved, the user agent must run the cache failure steps.
If the URL being processed was flagged as an "explicit entry" in file list, then categorize the entry as an explicit entry.
If the URL being processed was flagged as a "fallback entry" in file list, then categorize the entry as a fallback entry.
If the URL being processed was flagged as an "master entry" in file list, then categorize the entry as a master entry.
As an optimization, if the resource is an HTML or XML file whose document
element is an html element with a manifest attribute whose value doesn't match the manifest
URL of the application cache being processed, then the user agent should mark the entry as
being foreign.
For each cache host associated with an application cache in cache group, queue a progress post-load task to run these steps:
Let showProgress be the result of firing an
event named progress at the
ApplicationCache singleton of the cache host, using
ProgressEvent, with the cancelable
attribute initialized to true, the lengthComputable attribute initialized to
true, and the total and loaded attributes initialized to the number of files
in file list. [XHR]
If showProgress is true and the user agent shows caching progress, then display some sort of user interface indicating to the user that all the files have been downloaded.
Store the list of fallback namespaces, and the URLs of the fallback entries that they map to, in new cache.
Store the URLs that form the new online safelist in new cache.
Store the value of the new online safelist wildcard flag in new cache.
Store the value of the new cache mode flag in new cache.
For each entry in cache group's list of pending master entries, wait for the resource for this entry to have either completely downloaded or failed.
If the download failed (e.g. the server returns a 4xx or 5xx response, or there is a DNS error, the connection times out, or the user cancels the download), or if the resource is labeled with the "no-store" cache directive, then run these substeps:
Unassociate the Document for this entry from new
cache.
Queue a post-load task to run these steps:
Let showProgress be the result of firing
an event named error at the
ApplicationCache singleton of the Document for this entry, if there
still is one, with the cancelable attribute
initialized to true.
If showProgress is true and the user agent shows caching progress, then display some sort of user interface indicating to the user that the user agent failed to save the application for offline use.
If this is a cache attempt and this entry is the last entry in cache group's list of pending master entries, then run these further substeps:
Discard cache group and its only application cache, new cache.
If appropriate, remove any user interface indicating that an update for this cache is in progress.
Abort the application cache download process.
Otherwise, remove this entry from cache group's list of pending master entries.
Otherwise, store the resource for this entry in new cache, if it isn't already there, and categorize its entry as a master entry.
Let request be a new request whose
url is manifest URL, client is null, destination is the empty string,
referrer is "no-referrer",
synchronous flag is set, credentials
mode is "include", and whose use-URL-credentials
flag is set.
Let second manifest be the result of fetching request. HTTP caching semantics should again be honored for this request.
Since caching can be honored, authors are encouraged to avoid setting the cache headers on the manifest in such a way that the user agent would simply not contact the network for this second request; otherwise, the user agent would not notice if the cache had changed during the cache update process.
If the previous step failed for any reason, or if the fetching attempt involved a redirect, or if second manifest and manifest are not byte-for-byte identical, then schedule a rerun of the entire algorithm with the same parameters after a short delay, and run the cache failure steps.
Otherwise, store manifest in new cache, if it's not there already, and categorize its entry as the manifest.
Set the completeness flag of new cache to complete.
Let task list be an empty list of tasks.
If this is a cache attempt, then for each cache host associated with an application cache in cache group, create a task to run these steps and append it to task list:
Let showProgress be the result of firing an
event named cached at the
ApplicationCache singleton of the cache host, with the cancelable attribute initialized to true.
If showProgress is true and the user agent shows caching progress, then display some sort of user interface indicating to the user that the application has been cached and that they can now use it offline.
Otherwise, it is an upgrade attempt. For each cache host associated with an application cache in cache group, create a task to run these steps and append it to task list:
Let showProgress be the result of firing an
event named updateready at the
ApplicationCache singleton of the cache host, with the cancelable attribute initialized to true.
If showProgress is true and the user agent shows caching progress, then display some sort of user interface indicating to the user that a new version is available and that they can activate it by reloading the page.
If appropriate, remove any user interface indicating that an update for this cache is in progress.
Set the update status of cache group to idle.
For each task in task list, queue that task as a post-load task.
The cache failure steps are as follows:
Let task list be an empty list of tasks.
For each entry in cache group's list of pending master entries, run the following further substeps. These steps may be run in parallel for two or more entries at a time.
Wait for the resource for this entry to have either completely downloaded or failed.
Unassociate the Document for this entry from its application
cache, if it has one.
Create a task to run these steps and append it to task list:
Let showProgress be the result of firing
an event named error at the
ApplicationCache singleton of the Document for this entry, if there
still is one, with the cancelable attribute
initialized to true.
If showProgress is true and the user agent shows caching progress, then display some sort of user interface indicating to the user that the user agent failed to save the application for offline use.
For each cache host still associated with an application cache in cache group, create a task to run these steps and append it to task list:
Let showProgress be the result of firing an
event named error at the
ApplicationCache singleton of the cache host, with the cancelable attribute initialized to true.
If showProgress is true and the user agent shows caching progress, then display some sort of user interface indicating to the user that the user agent failed to save the application for offline use.
Empty cache group's list of pending master entries.
If cache group has an application cache whose completeness flag is incomplete, then discard that application cache.
If appropriate, remove any user interface indicating that an update for this cache is in progress.
Let the status of cache group be idle.
If this was a cache attempt, discard cache group altogether.
For each task in task list, queue that task as a post-load task.
Abort the application cache download process.
Attempts to fetch resources as part of the application cache download process may be done with cache-defeating semantics, to avoid problems with stale or inconsistent intermediary caches.
User agents may invoke the application cache download process, in the background, for any application cache group, at any time (with no cache host). This allows user agents to keep caches primed and to update caches even before the user visits a site.
Each Document has a list of pending application cache download process
tasks that is used to delay events fired by the algorithm above until the document's load event has fired. When the Document is created, the
list must be empty.
When the steps above say to queue a post-load task task, where
task is a task that dispatches an event on a
target ApplicationCache object target, the user agent must run
the appropriate steps from the following list:
Queue the task task.
Add task to target's node document's list of pending application cache download process tasks.
When the steps above say to queue a progress post-load task task, where
task is a task that dispatches an event on a
target ApplicationCache object target, the user agent must run
the following steps:
If there is a task in target's node document's list of pending application cache download process tasks that is labeled as a progress task, then remove that task from the list.
Label task as a progress task.
Queue a post-load task task.
The task source for these tasks is the networking task source.
When the application cache selection algorithm
algorithm is invoked with a Document document and optionally a
manifest URL manifest URL, the user agent must run the first
applicable set of steps from the following list:
Mark the entry for the resource from which document was taken in the application cache from which it was loaded as foreign.
Restart the current navigation from the top of the navigation algorithm, undoing any changes that were made as part of the initial load (changes can be avoided by ensuring that the step to update the session history with the new page is only ever completed after this application cache selection algorithm is run, though this is not required).
The navigation will not result in the same resource being loaded, because "foreign" entries are never picked during navigation.
User agents may notify the user of the inconsistency between the cache manifest and the document's own metadata, to aid in application development.
Associate document with the application cache from which it was loaded. Invoke, in the background, the application cache download process for that application cache's application cache group, with document as the cache host.
GET`, and, there is a
manifest URL, and manifest URL has the same origin as
documentInvoke, in the background, the application cache download process for manifest URL, with document as the cache host and with the resource from which document was parsed as the master resource.
If there are relevant application caches that are identified by a URL with the same origin as the URL of document, and that have this URL as one of their entries, excluding entries marked as foreign, then the user agent should use the most appropriate application cache of those that match as an HTTP cache for any subresource loads. User agents may also have other caches in place that are also honored.
The Document is not associated with any application cache.
If there was a manifest URL, the user agent may report to the user that it was ignored, to aid in application development.
If "AppCache" is not removed as a feature this section needs to be integrated into the Fetch standard.
When a cache host is associated with an application cache whose completeness flag is complete, any and all loads for resources related to that cache host other than those for child browsing contexts must go through the following steps instead of immediately invoking the mechanisms appropriate to that resource's scheme:
If the resource is not to be fetched using the GET method, or if applying the URL parser algorithm to both its URL and the application cache's manifest's URL results in two URL records with different scheme components, then fetch the resource normally and abort these steps.
If the resource's URL is a master entry, the manifest, an explicit entry, or a fallback entry in the application cache, then get the resource from the cache (instead of fetching it), and abort these steps.
If there is an entry in the application cache's online safelist that has the same origin as the resource's URL and that is a prefix match for the resource's URL, then fetch the resource normally and abort these steps.
If the resource's URL has the same origin as the manifest's URL, and there is a fallback namespace f in the application cache that is a prefix match for the resource's URL, then:
Fetch the resource normally. If this results in a redirect to a resource with another origin (indicative of a captive portal), or a 4xx or 5xx status code, or if there were network errors (but not if the user canceled the download), then instead get, from the cache, the resource of the fallback entry corresponding to the fallback namespace f. Abort these steps.
If the application cache's online safelist wildcard flag is open, then fetch the resource normally and abort these steps.
Fail the resource load as if there had been a generic network error.
The above algorithm ensures that so long as the online safelist wildcard flag is blocking, resources that are not present in the manifest will always fail to load (at least, after the application cache has been primed the first time), making the testing of offline applications simpler.
As a general rule, user agents should not expire application caches, except on request from the user, or after having been left unused for an extended period of time.
Application caches and cookies have similar implications with respect to privacy (e.g. if the site can identify the user when providing the cache, it can store data in the cache that can be used for cookie resurrection). Implementors are therefore encouraged to expose application caches in a manner related to HTTP cookies, allowing caches to be expunged together with cookies and other origin-specific data.
For example, a user agent could have a "delete site-specific data" feature that clears all cookies, application caches, local storage, databases, etc, from an origin all at once.
User agents should consider applying constraints on disk usage of application caches, and care should be taken to ensure that the restrictions cannot be easily worked around using subdomains.
User agents should allow users to see how much space each domain is using, and may offer the user the ability to delete specific application caches.
For predictability, quotas should be based on the uncompressed size of data stored.
How quotas are presented to the user is not defined by this specification. User agents are encouraged to provide features such as allowing a user to indicate that certain sites are trusted to use more than the default quota, e.g. by presenting a non-modal user interface while a cache is being updated, or by having an explicit safelist in the user agent's configuration interface.
This section is non-normative.
The main risk introduced by offline application caches is that an injection attack can be elevated into persistent site-wide page replacement. This attack involves using an injection vulnerability to upload two files to the victim site. The first file is an application cache manifest consisting of just a fallback entry pointing to the second file, which is an HTML page whose manifest is declared as that first file. Once the user has been directed to that second file, all subsequent accesses to any file covered by the given fallback namespace while either the user or the site is offline will instead show that second file. Targeted denial-of-service attacks or cookie bombing attacks (where the client is made to send so many cookies that the server refuses to process the request) can be used to ensure that the site appears offline.
To mitigate this, manifests can only specify fallbacks that are in the same path as the manifest itself. This means that a content injection upload vulnerability in a particular directory on a server can only be escalated to a take-over of that directory and its subdirectories. If there is no way to inject a file into the root directory, the entire site cannot be taken over.
If a site has been attacked in this way, simply removing the offending manifest might eventually clear the problem, since the next time the manifest is updated, a 404 error will be seen, and the user agent will clear the cache. "Eventually" is the key word here, however; while the attack on the user or server is ongoing, such that connections from an affected user to the affected site are blocked, the user agent will simply assume that the user is offline and will continue to use the hostile manifest. Unfortunately, if a cookie bombing attack has also been used, merely removing the manifest is insufficient; in addition, the server has to be configured to return a 404 or 410 response instead of the 413 "Request Entity Too Large" response.
TLS does not inherently protect a site from this attack, since the attack relies on content being served from the server itself. Not using application caches also does not prevent this attack, since the attack relies on an attacker-provided manifest.
interface ApplicationCache : EventTarget {
// update status
const unsigned short UNCACHED = 0;
const unsigned short IDLE = 1;
const unsigned short CHECKING = 2;
const unsigned short DOWNLOADING = 3;
const unsigned short UPDATEREADY = 4;
const unsigned short OBSOLETE = 5;
readonly attribute unsigned short status;
// updates
void update();
void abort();
void swapCache();
// events
attribute EventHandler onchecking;
attribute EventHandler onerror;
attribute EventHandler onnoupdate;
attribute EventHandler ondownloading;
attribute EventHandler onprogress;
attribute EventHandler onupdateready;
attribute EventHandler oncached;
attribute EventHandler onobsolete;
};
applicationCacheReturns the ApplicationCache object that applies to the active
document of that Window.
statusReturns the current status of the application cache, as given by the constants defined below.
update()Invokes the application cache download process.
Throws an "InvalidStateError" DOMException if there is
no application cache to update.
Calling this method is not usually necessary, as user agents will generally take care of updating application caches automatically.
The method can be useful in situations such as long-lived applications. For example, a Web mail application might stay open in a browser tab for weeks at a time. Such an application could want to test for updates each day.
abort()Cancels the application cache download process.
This method is intended to be used by Web application showing their own caching progress UI, in case the user wants to stop the update (e.g. because bandwidth is limited).
swapCache()Switches to the most recent application cache, if there is a newer one. If there isn't,
throws an "InvalidStateError" DOMException.
This does not cause previously-loaded resources to be reloaded; for example, images do not suddenly get reloaded and style sheets and scripts do not get reparsed or reevaluated. The only change is that subsequent requests for cached resources will obtain the newer copies.
The updateready event will fire before this
method can be called. Once it fires, the Web application can, at its leisure, call this method
to switch the underlying cache to the one with the more recent updates. To make proper use of
this, applications have to be able to bring the new features into play; for example, reloading
scripts to enable new features.
An easier alternative to swapCache() is just to
reload the entire page at a time suitable for the user, using location.reload().
There is a one-to-one mapping from cache hosts to
ApplicationCache objects. The applicationCache attribute on Window
objects must return the ApplicationCache object associated with the
Window object's active document.
A Document has an associated ApplicationCache object
even if that cache host has no actual application cache.
The status attribute, on getting, must
return the current state of the application cache that the
ApplicationCache object's cache host is associated with, if any. This
must be the appropriate value from the following list:
UNCACHED (numeric value 0)The ApplicationCache object's cache host is not associated with
an application cache at this time.
IDLE (numeric value 1)The ApplicationCache object's cache host is associated with an
application cache whose application cache group's update status is idle, and that application
cache is the newest cache in its
application cache group, and the application cache group is not marked
as obsolete.
CHECKING (numeric value 2)The ApplicationCache object's cache host is associated with an
application cache whose application cache group's update status is checking.
DOWNLOADING (numeric value 3)The ApplicationCache object's cache host is associated with an
application cache whose application cache group's update status is downloading.
UPDATEREADY (numeric value 4)The ApplicationCache object's cache host is associated with an
application cache whose application cache group's update status is idle, and whose application
cache group is not marked as obsolete, but
that application cache is not the newest cache in its group.
OBSOLETE (numeric value 5)The ApplicationCache object's cache host is associated with an
application cache whose application cache group is marked as obsolete.
If the update() method is invoked, the user
agent must invoke the application cache download process, in the background, for the
application cache group of the application cache with which the
ApplicationCache object's cache host is associated, but without giving
that cache host to the algorithm. If there is no such application cache,
or if its application cache group is marked as obsolete, then the method must throw an
"InvalidStateError" DOMException instead.
If the abort() method is invoked, the user
agent must send a signal to the current application cache download process
for the application cache group of the application cache with which the
ApplicationCache object's cache host is associated, if any. If there is
no such application cache, or it does not have a current application cache
download process, then do nothing.
If the swapCache() method is invoked,
the user agent must run the following steps:
Check that ApplicationCache object's cache host is associated
with an application cache. If it is not, then throw an
"InvalidStateError" DOMException and abort these
steps.
Let cache be the application cache with which the
ApplicationCache object's cache host is associated. (By definition,
this is the same as the one that was found in the previous step.)
If cache's application cache group is marked as obsolete, then unassociate the
ApplicationCache object's cache host from cache and
abort these steps. (Resources will now load from the network instead of the cache.)
Check that there is an application cache in the same application cache group
as cache whose completeness
flag is complete and that is newer than
cache. If there is not, then throw an "InvalidStateError"
DOMException exception and abort these steps.
Let new cache be the newest application cache in the same application cache group as cache whose completeness flag is complete.
Unassociate the ApplicationCache object's cache host from cache and instead associate it with new cache.
The following are the event handlers (and their corresponding event handler event types) that must be
supported, as event handler IDL attributes, by all objects implementing the
ApplicationCache interface:
| Event handler | Event handler event type |
|---|---|
onchecking | checking
|
onerror | error
|
onnoupdate | noupdate
|
ondownloading | downloading
|
onprogress | progress
|
onupdateready | updateready
|
oncached | cached
|
onobsolete | obsolete
|
Support: online-statusChrome for Android 56+Chrome 14+UC Browser for Android (limited) 11+iOS Safari 4.2+Firefox 41+IE 9+Samsung Internet 4+Opera Mini NoneAndroid Browser 2.3+Safari 5+Edge 12+Opera 15+
Source: caniuse.com
[NoInterfaceObject, Exposed=(Window,Worker)]
interface NavigatorOnLine {
readonly attribute boolean onLine;
};
navigator . onLineReturns false if the user agent is definitely offline (disconnected from the network). Returns true if the user agent might be online.
The events online and offline are fired when the value of this attribute changes.
The navigator.onLine attribute must return
false if the user agent will not contact the network when the user follows links or when a script
requests a remote page (or knows that such an attempt would fail), and must return true
otherwise.
When the value that would be returned by the navigator.onLine attribute of a Window or
WorkerGlobalScope changes from true to false, the user agent must queue a
task to fire an event named offline at the Window or WorkerGlobalScope
object.
On the other hand, when the value that would be returned by the navigator.onLine attribute of a Window or
WorkerGlobalScope changes from false to true, the user agent must queue a
task to fire an event named online at the Window or WorkerGlobalScope
object.
The task source for these tasks is the networking task source.
This attribute is inherently unreliable. A computer can be connected to a network without having Internet access.
In this example, an indicator is updated as the browser goes online and offline.
<!DOCTYPE HTML>
<html lang="en">
<head>
<title>Online status</title>
<script>
function updateIndicator() {
document.getElementById('indicator').textContent = navigator.onLine ? 'online' : 'offline';
}
</script>
</head>
<body onload="updateIndicator()" ononline="updateIndicator()" onoffline="updateIndicator()">
<p>The network is: <span id="indicator">(state unknown)</span>
</body>
</html>