systrace/catapult/third_party/polymer/components/iron-a11y-announcer/iron-a11y-announcer.html

<!--
@license
Copyright (c) 2015 The Polymer Project Authors. All rights reserved.
This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
Code distributed by Google as part of the polymer project is also
subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
-->

<link rel="import" href="../polymer/polymer.html">

<!--
`iron-a11y-announcer` is a singleton element that is intended to add a11y
to features that require on-demand announcement from screen readers. In
order to make use of the announcer, it is best to request its availability
in the announcing element.

Example:

    Polymer({

      is: 'x-chatty',

      attached: function() {
        // This will create the singleton element if it has not
        // been created yet:
        Polymer.IronA11yAnnouncer.requestAvailability();
      }
    });

After the `iron-a11y-announcer` has been made available, elements can
make announces by firing bubbling `iron-announce` events.

Example:

    this.fire('iron-announce', {
      text: 'This is an announcement!'
    }, { bubbles: true });

Note: announcements are only audible if you have a screen reader enabled.

@group Iron Elements
@demo demo/index.html
-->

<dom-module id="iron-a11y-announcer">
  <template>
    <style>
      :host {
        display: inline-block;
        position: fixed;
        clip: rect(0px,0px,0px,0px);
      }
    </style>
    <div aria-live$="[[mode]]">[[_text]]</div>
  </template>
</dom-module>
<script>
'use strict';
(function() {
  'use strict';
  Polymer.IronA11yAnnouncer = Polymer({
    is: 'iron-a11y-announcer',

    properties: {

      /**
        * The value of mode is used to set the `aria-live` attribute
        * for the element that will be announced. Valid values are: `off`,
        * `polite` and `assertive`.
        */
      mode: {
        type: String,
        value: 'polite'
      },

      _text: {
        type: String,
        value: ''
      }
    },

    created: function() {
      if (!Polymer.IronA11yAnnouncer.instance) {
        Polymer.IronA11yAnnouncer.instance = this;
      }

      document.body.addEventListener('iron-announce', this._onIronAnnounce.bind(this));
    },

    /**
      * Cause a text string to be announced by screen readers.
      *
      * @param {string} text The text that should be announced.
      */
    announce: function(text) {
      this._text = '';
      this.async(function() {
        this._text = text;
      }, 100);
    },

    _onIronAnnounce: function(event) {
      if (event.detail && event.detail.text) {
        this.announce(event.detail.text);
      }
    }
  });

  Polymer.IronA11yAnnouncer.instance = null;

  Polymer.IronA11yAnnouncer.requestAvailability = function() {
    if (!Polymer.IronA11yAnnouncer.instance) {
      Polymer.IronA11yAnnouncer.instance = document.createElement('iron-a11y-announcer');
    }

    document.body.appendChild(Polymer.IronA11yAnnouncer.instance);
  };
})();

</script>