Creating options page and storing preferences.

chrome/browser/resources/chromeos/switch_access/prefs.js

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+/**
+ * Class to manage user preferences.
+ *
+ * @constructor
+ */
+let SwitchAccessPrefs = function() {
+  /**
+   * User preferences, initially set to the default preference values.
+   *
+   * @private
+   */
+  this.prefs_ = Object.assign({}, this.DEFAULT_PREFS);
+  this.loadPrefs_();
+  chrome.storage.onChanged.addListener(this.handleStorageChange_.bind(this));
+};
+
+SwitchAccessPrefs.prototype = {
+  /**
+   * Asynchronously load the current preferences from chrome.storage.sync and
+   * store them in this.prefs_.
+   *
+   * @private
+   */
+  loadPrefs_: function() {
+    let defaultKeys = Object.keys(this.DEFAULT_PREFS);
+    chrome.storage.sync.get(defaultKeys, function(loadedPrefs) {
+      let loadedKeys = Object.keys(loadedPrefs);
+      if (loadedKeys.length > 0) {
+        for (let key of loadedKeys) {
+          this.prefs_[key] = loadedPrefs[key];
+        }
+        let event = new CustomEvent('prefsUpdate', {'detail': loadedPrefs});
+        document.dispatchEvent(event);
+      }
+    }.bind(this));
+  },
+
+  /**
+   * Store any changes to chrome.storage.sync in this.prefs_.
+   *
+   * @param {!Object} changes
+   * @param {string} areaName
+   * @private
+   */
+  handleStorageChange_: function(changes, areaName) {
+    for (let key of Object.keys(changes)) {
+      // If pref change happened on same device, prefs will already be updated,
+      // so this will have no effect.
+      this.prefs_[key] = changes[key].newValue;
+      changes[key] = changes[key].newValue;
+    }
+
+    let event = new CustomEvent('prefsUpdate', {'detail': changes});
+    document.dispatchEvent(event);
+  },
+
+  /**
+   * Set the value of the preference |key| to |value|.
+   *
+   * @param {string} key
+   * @param {boolean|string|number} value
+   */
+  setPref: function(key, value) {
+    let pref = {};
+    pref[key] = value;
+    chrome.storage.sync.set(pref);
+    this.prefs_[key] = value;
+  },
+
+  /**
+   * Get all user preferences.
+   */
+  getPrefs: function() {
+    return Object.assign({}, this.prefs_);
+  },
+
+  /**
+   * The default value of all preferences. All preferences should be primitives
+   * to prevent changes to default values.
+   *
+   * @const
+   */
+  DEFAULT_PREFS: {
+    'enableAutoScan': false,
+    'autoScanTime': .75
+  }
+};