Move Add-on SDK source to toolkit/jetpack

toolkit/jetpack/sdk/event/target.js

@@ -0,0 +1,74 @@
+/* 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": "stable"
+};
+
+const { on, once, off, setListeners } = require('./core');
+const { method, chainable } = require('../lang/functional/core');
+const { Class } = require('../core/heritage');
+
+/**
+ * `EventTarget` is an exemplar for creating an objects that can be used to
+ * add / remove event listeners on them. Events on these objects may be emitted
+ * via `emit` function exported by 'event/core' module.
+ */
+const EventTarget = Class({
+  /**
+   * Method initializes `this` event source. It goes through properties of a
+   * given `options` and registers listeners for the ones that look like an
+   * event listeners.
+   */
+  /**
+   * Method initializes `this` event source. It goes through properties of a
+   * given `options` and registers listeners for the ones that look like an
+   * event listeners.
+   */
+  initialize: function initialize(options) {
+    setListeners(this, options);
+  },
+  /**
+   * Registers an event `listener` that is called every time events of
+   * specified `type` are emitted.
+   * @param {String} type
+   *    The type of event.
+   * @param {Function} listener
+   *    The listener function that processes the event.
+   * @example
+   *      worker.on('message', function (data) {
+   *        console.log('data received: ' + data)
+   *      })
+   */
+  on: chainable(method(on)),
+  /**
+   * Registers an event `listener` that is called once the next time an event
+   * of the specified `type` is emitted.
+   * @param {String} type
+   *    The type of the event.
+   * @param {Function} listener
+   *    The listener function that processes the event.
+   */
+  once: chainable(method(once)),
+  /**
+   * Removes an event `listener` for the given event `type`.
+   * @param {String} type
+   *    The type of event.
+   * @param {Function} listener
+   *    The listener function that processes the event.
+   */
+  removeListener: function removeListener(type, listener) {
+    // Note: We can't just wrap `off` in `method` as we do it for other methods
+    // cause skipping a second or third argument will behave very differently
+    // than intended. This way we make sure all arguments are passed and only
+    // one listener is removed at most.
+    off(this, type, listener);
+    return this;
+  },
+  // but we can wrap `off` here, as the semantics are the same
+  off: chainable(method(off))
+
+});
+exports.EventTarget = EventTarget;