1 /* This Source Code Form is subject to the terms of the Mozilla Public
2 * License, v. 2.0. If a copy of the MPL was not distributed with this
3 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
5 // This file is loaded into the browser window scope.
6 /* eslint-env mozilla/browser-window */
9 * Utility functions for UI accessibility.
14 * Announce a message to the user.
15 * This should only be used when something happens that is important to the
16 * user and will be noticed visually, but is not related to the focused
17 * control and is not a pop-up such as a doorhanger.
18 * For example, this could be used to indicate that Reader View is available
19 * or that Firefox is making a recommendation via the toolbar.
20 * This must be used with caution, as it can create unwanted verbosity and
21 * can thus hinder rather than help users if used incorrectly.
22 * Please only use this after consultation with the Mozilla accessibility
24 * @param {object} [options]
25 * @param {string} [options.id] The Fluent id of the message to announce. The
26 * ftl file must already be included in browser.xhtml. This must be
27 * specified unless a raw message is specified instead.
28 * @param {object} [options.args] Arguments for the Fluent message.
29 * @param {string} [options.raw] The raw, already localized message to
30 * announce. You should generally prefer a Fluent id instead, but in
31 * rare cases, this might not be feasible.
33 async announce({ id = null, args = {}, raw = null } = {}) {
34 if ((!id && !raw) || (id && raw)) {
35 throw new Error("One of raw or id must be specified.");
38 // Cancel a previous pending call if any.
39 if (this._cancelAnnounce) {
40 this._cancelAnnounce();
41 this._cancelAnnounce = null;
47 this._cancelAnnounce = () => (cancel = true);
48 message = await document.l10n.formatValue(id, args);
50 // announce() was called again while we were waiting for translation.
53 // No more async operations from this point.
54 this._cancelAnnounce = null;
56 // We run fully synchronously if a raw message is provided.
60 // For now, we don't use source, but it might be useful in future.
61 // For example, we might use it when we support announcement events on
62 // more platforms or it could be used to have a keyboard shortcut which
63 // focuses the last element to announce a message.
64 let live = document.getElementById("a11y-announcement");
65 // We use role="alert" because JAWS doesn't support aria-live in browser
67 // Gecko a11y needs an insertion to trigger an alert event. This is why
68 // we can't just use aria-label on the alert.
69 if (live.firstChild) {
70 live.firstChild.remove();
72 let label = document.createElement("label");
73 label.setAttribute("aria-label", message);
74 live.appendChild(label);