Andreas Hocevar
124 lines
4.1 KiB
JavaScript
124 lines
4.1 KiB
JavaScript
// Copyright 2007 The Closure Library Authors. All Rights Reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS-IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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/**
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* @fileoverview Announcer that allows messages to be spoken by assistive
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* technologies.
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*/
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goog.provide('goog.a11y.aria.Announcer');
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goog.require('goog.Disposable');
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goog.require('goog.Timer');
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goog.require('goog.a11y.aria');
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goog.require('goog.a11y.aria.LivePriority');
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goog.require('goog.a11y.aria.State');
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goog.require('goog.dom');
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goog.require('goog.dom.TagName');
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goog.require('goog.object');
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/**
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* Class that allows messages to be spoken by assistive technologies that the
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* user may have active.
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*
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* @param {goog.dom.DomHelper=} opt_domHelper DOM helper.
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* @constructor
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* @extends {goog.Disposable}
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* @final
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*/
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goog.a11y.aria.Announcer = function(opt_domHelper) {
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goog.a11y.aria.Announcer.base(this, 'constructor');
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/**
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* @type {goog.dom.DomHelper}
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* @private
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*/
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this.domHelper_ = opt_domHelper || goog.dom.getDomHelper();
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/**
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* Map of priority to live region elements to use for communicating updates.
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* Elements are created on demand.
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* @type {Object<goog.a11y.aria.LivePriority, !Element>}
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* @private
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*/
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this.liveRegions_ = {};
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};
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goog.inherits(goog.a11y.aria.Announcer, goog.Disposable);
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/** @override */
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goog.a11y.aria.Announcer.prototype.disposeInternal = function() {
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goog.object.forEach(
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this.liveRegions_, this.domHelper_.removeNode, this.domHelper_);
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this.liveRegions_ = null;
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this.domHelper_ = null;
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goog.a11y.aria.Announcer.base(this, 'disposeInternal');
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};
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/**
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* Announce a message to be read by any assistive technologies the user may
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* have active.
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* @param {string} message The message to announce to screen readers.
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* @param {goog.a11y.aria.LivePriority=} opt_priority The priority of the
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* message. Defaults to POLITE.
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*/
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goog.a11y.aria.Announcer.prototype.say = function(message, opt_priority) {
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var priority = opt_priority || goog.a11y.aria.LivePriority.POLITE;
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var liveRegion = this.getLiveRegion_(priority);
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// Resets text content to force a DOM mutation (so that the setTextContent
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// post-timeout function will be noticed by the screen reader). This is to
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// avoid the problem of when the same message is "said" twice, which doesn't
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// trigger a DOM mutation.
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goog.dom.setTextContent(liveRegion, '');
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// Uses non-zero timer to make VoiceOver and NVDA work
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goog.Timer.callOnce(function() {
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goog.dom.setTextContent(liveRegion, message);
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}, 1);
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};
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/**
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* Returns an aria-live region that can be used to communicate announcements.
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* @param {!goog.a11y.aria.LivePriority} priority The required priority.
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* @return {!Element} A live region of the requested priority.
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* @private
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*/
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goog.a11y.aria.Announcer.prototype.getLiveRegion_ = function(priority) {
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var liveRegion = this.liveRegions_[priority];
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if (liveRegion) {
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// Make sure the live region is not aria-hidden.
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goog.a11y.aria.removeState(liveRegion, goog.a11y.aria.State.HIDDEN);
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return liveRegion;
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}
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liveRegion = this.domHelper_.createElement(goog.dom.TagName.DIV);
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// Note that IE has a habit of declaring things that aren't display:none as
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// invisible to third-party tools like JAWs, so we can't just use height:0.
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liveRegion.style.position = 'absolute';
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liveRegion.style.top = '-1000px';
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liveRegion.style.height = '1px';
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liveRegion.style.overflow = 'hidden';
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goog.a11y.aria.setState(liveRegion, goog.a11y.aria.State.LIVE,
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priority);
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goog.a11y.aria.setState(liveRegion, goog.a11y.aria.State.ATOMIC,
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'true');
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this.domHelper_.getDocument().body.appendChild(liveRegion);
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this.liveRegions_[priority] = liveRegion;
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return liveRegion;
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};
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