chrome/browser/resources/settings/pref_tracker/pref_tracker.js

   1 // Copyright 2015 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 /**
   6  * @fileoverview
   7  * `cr-settings-pref-tracker` is a utility element used to track the
   8  * initialization of a specified preference and throw an error if the pref
   9  * is not defined after prefs have all been fetched.
  10  *
  11  * Example:
  12  *
  13  *    <cr-settings-pref-tracker pref="{{prefs.settings.foo.bar}}">
  14  *    </cr-settings-pref-tracker>
  15  *
  16  * @element cr-settings-pref-tracker
  17  */
  18 (function() {
  19
  20   /**
  21    * An array of all the tracker instances.
  22    * @type {!Array<!CrSettingsPrefTrackerElement>}
  23    */
  24   var instances = [];
  25
  26   /**
  27    * Validates all tracker instances.
  28    * @private
  29    */
  30   var validateAll_ = function() {
  31     instances.forEach(function(tracker) {
  32       tracker.validate_();
  33     });
  34   };
  35
  36   document.addEventListener(CrSettingsPrefs.INITIALIZED, validateAll_);
  37
  38   Polymer({
  39     is: 'cr-settings-pref-tracker',
  40
  41     properties: {
  42       /**
  43        * The Preference object being tracked.
  44        * @type {?PrefObject}
  45        */
  46       pref: {
  47         type: Object,
  48         observer: 'validate_',
  49       },
  50     },
  51
  52     /** @override */
  53     ready: function() {
  54       this.validate_();
  55
  56       instances.push(this);
  57     },
  58
  59     /**
  60      * Throws an error if prefs are initialized and the tracked pref is not
  61      * found.
  62      * @private
  63      */
  64     validate_: function() {
  65       this.async(function() {
  66         // Note that null == undefined.
  67         if (CrSettingsPrefs.isInitialized && this.pref == null) {
  68           // HACK ALERT: This is the best clue we have as to the pref key for
  69           // this tracker. This value should not be relied upon anywhere or
  70           // actually used besides for this error message.
  71           var parentControlHTML = this.parentNode && this.parentNode.host &&
  72               this.parentNode.host.outerHTML;
  73
  74           throw new Error('Pref not found. Parent control:' +
  75               (parentControlHTML || 'Unknown'));
  76         }
  77       });
  78     },
  79   });
  80 })();