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('cr-settings-pref-tracker', {
  39     publish: {
  40       /**
  41        * The Preference object being tracked.
  42        *
  43        * @attribute pref
  44        * @type {Object}
  45        * @default null
  46        */
  47       pref: null,
  48     },
  49
  50     observe: {
  51       pref: 'validate_',
  52     },
  53
  54     /** @override */
  55     ready: function() {
  56       this.validate_();
  57
  58       instances.push(this);
  59     },
  60
  61     /**
  62      * Throws an error if prefs are initialized and the tracked pref is not
  63      * found.
  64      * @private
  65      */
  66     validate_: function() {
  67       this.async(function() {
  68         // Note that null == undefined.
  69         if (CrSettingsPrefs.isInitialized && this.pref == null) {
  70           // HACK ALERT: This is the best clue we have as to the pref key for
  71           // this tracker. This value should not be relied upon anywhere or
  72           // actually used besides for this error message.
  73           var keyHint = '';
  74           var parentPrefString = this.parentNode && this.parentNode.host &&
  75               this.parentNode.host.getAttribute('pref');
  76           if (parentPrefString) {
  77             keyHint = parentPrefString.match(/{{([a-z._]+)}}/)[1];
  78           }
  79
  80           throw new Error('Pref not found. Key Hint: ' + keyHint);
  81         }
  82       });
  83     },
  84   });
  85 })();