1 files changed, 61 insertions, 0 deletions
diff --git a/toolkit/jetpack/sdk/preferences/event-target.js b/toolkit/jetpack/sdk/preferences/event-target.js
new file mode 100644
index 000000000..b64ba303c
--- /dev/null
+++ b/toolkit/jetpack/sdk/preferences/event-target.js
@@ -0,0 +1,61 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+'use strict';
+
+module.metadata = {
+  "stability": "unstable"
+};
+
+const { Cc, Ci } = require('chrome');
+const { Class } = require('../core/heritage');
+const { EventTarget } = require('../event/target');
+const { Branch } = require('./service');
+const { emit, off } = require('../event/core');
+const { when: unload } = require('../system/unload');
+
+const prefTargetNS = require('../core/namespace').ns();
+
+const PrefsTarget = Class({
+  extends: EventTarget,
+  initialize: function(options) {
+    options = options || {};
+    EventTarget.prototype.initialize.call(this, options);
+
+    let branchName = options.branchName || '';
+    let branch = Cc["@mozilla.org/preferences-service;1"].
+        getService(Ci.nsIPrefService).
+        getBranch(branchName).
+        QueryInterface(Ci.nsIPrefBranch2);
+    prefTargetNS(this).branch = branch;
+
+    // provides easy access to preference values
+    this.prefs = Branch(branchName);
+
+    // start listening to preference changes
+    let observer = prefTargetNS(this).observer = onChange.bind(this);
+    branch.addObserver('', observer, false);
+
+    // Make sure to destroy this on unload
+    unload(destroy.bind(this));
+  }
+});
+exports.PrefsTarget = PrefsTarget;
+
+/* HELPERS */
+
+function onChange(subject, topic, name) {
+  if (topic === 'nsPref:changed') {
+    emit(this, name, name);
+    emit(this, '', name);
+  }
+}
+
+function destroy() {
+  off(this);
+
+  // stop listening to preference changes
+  let branch = prefTargetNS(this).branch;
+  branch.removeObserver('', prefTargetNS(this).observer, false);
+  prefTargetNS(this).observer = null;
+}