aom

Can I Use Accessibility Object Model (AOM)

Track the implementation status of the AOM in various browsers.

How to enable AOM

Chrome:

For AccessibleNode/ComputedAccessibleNode-related features:
--enable-blink-features=AccessibilityObjectModel

For web platform related features: Browse to chrome://flags, enable enable-experimental-web-platform-features.

Safari Technology Preview:

Develop > Experimental Features > Accessibility Object Model

Firefox:

about:config accessibility.AOM.enabled = true

Summary

Last updated: July 9, 2019

  Chrome Safari Firefox
Phase 1: Reflect ARIA attributes on DOM nodes. Yes Yes No
Phase 1: Reflect element references for IDREF attributes No No No
Phase 1: Custom element semantics on ElementInternals Yes No No
Phase 2: Generated fallback events for AT actions No No No
Phase 2: New InputEvent types No No No
Phase 3: Build virtual accessible nodes. Yes, out-of-date syntax No No
Phase 4: Query computed accessibility tree. Yes, out-of-date syntax No Yes, out-of-date syntax

Phase 1: Reflect ARIA attributes on DOM nodes.

Available in Safari; behind --experimental-web-platform-features flag in Chrome

element.role = "button";
element.ariaLabel = "Click Me";

Phase 1: Reflect element references for IDREF attributes

Not yet implemented

Spec: https://whatpr.org/html/3917/common-dom-interfaces.html#reflecting-content-attributes-in-idl-attributes:element

element.ariaActiveDescendantElement = otherElement;
element.ariaLabelledByElements = [ anotherElement, someOtherElement ];

Phase 1: Custom element semantics on ElementInternals

Currently being implemented in Chrome: https://chromestatus.com/feature/5962105603751936

Spec: https://whatpr.org/html/4658/custom-elements.html#native-accessibility-semantics-map

class CustomTab extends HTMLElement {
  constructor() {
    super();
    this._internals = customElements.createInternals(this);
    this._internals.role = "tab";
  }

  // Observe the custom "active" attribute.
  static get observedAttributes() { return ["active"]; }

  connectedCallback() {
    this._tablist = this.parentElement;
  }

  setTabPanel(tabpanel) {
    if (tabpanel.localName !== "custom-tabpanel" || tabPanel.id === "")
      return;  // fail silently

    this._tabpanel = tabpanel;
    tabpanel.setTab(this);
    this._internals.ariaControls = tabPanel;    // does not reflect
  }

  // ... setters/getters for custom properties which reflect to attributes

  attributeChangedCallback(name, oldValue, newValue) {
    switch(name) {
      case "active":
        let active = (newValue != null);
        this._tabpanel.shown = active;

        // When the custom "active" attribute changes,
        // keep the accessible "selected" state in sync.
        this._internals.ariaSelected = (newValue !== null);

        if (selected)
          this._tablist.setSelectedTab(this);  // ensure no other tab has "active" set
        break;
    }
  }
}

Phase 2: Generated fallback events for AT actions

(Not yet specced/implemented)

customSlider.addEventListener('keydown', (event) => {
  switch (event.code) {
  case "ArrowUp":
    customSlider.value += 1;
    return;
  case "ArrowDown":
    customSlider.value -= 1;
    return;
});

Phase 2: New InputEvent types

(Not yet specced/implemented)

customSlider.addEventListener("increment", function(event) {
  customSlider.value += 1;
});

customSlider.addEventListener("decrement", function(event) {
  customSlider.value -= 1;
});

Phase 3: Build virtual accessible nodes.

Chrome (out of date syntax, pass --enable-blink-features=AccessibilityObjectModel):

var listitem = new AccessibleNode();
listitem.role = "listitem";
listitem.offsetParent = list.accessibleNode;
listitem.offsetTop = 32;
listitem.offsetLeft = 0;
listitem.offsetWidth = 200;
listitem.offsetHeight = 16;

// future syntax may be: list.attachAccessibleRoot().appendChild
list.accessibleNode.appendChild(listitem);  

Phase 4: Query computed accessibility tree.

Chrome (speculative syntax, pass --enable-blink-features=AccessibilityObjectModel):

var c = await window.getComputedAccessibleNode(element);
console.log(c.role);
console.log(c.label);

Firefox (out of date syntax):

console.log(element.accessibleNode.computedRole);