Open Source Monorail

appengine/monorail/static/js/graveyard/listen.js

+/* Copyright 2016 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 or at
+ * https://developers.google.com/open-source/licenses/bsd
+ */
+
+var listen;
+var unlisten;
+var unlistenByKey;
+
+(function() {
+  var listeners = {};
+  var nextId = 0;
+
+  function getHashCode_(obj) {
+    if (obj.listen_hc_ == null) {
+      obj.listen_hc_ = ++nextId;
+    }
+    return obj.listen_hc_;
+  }
+
+  /**
+   * Takes a node, event, listener, and capture flag to create a key
+   * to identify the tuple in the listeners hash.
+   *
+   * @param {Element} node The node to listen to events on.
+   * @param {string} event The name of the event without the "on" prefix.
+   * @param {Function} listener A function to call when the event occurs.
+   * @param {boolean} opt_useCapture In DOM-compliant browsers, this determines
+   *                                 whether the listener is fired during the
+   *                                 capture or bubble phase of the event.
+   * @return {string} key to identify this tuple in the listeners hash.
+   */
+  function createKey_(node, event, listener, opt_useCapture) {
+    var nodeHc = getHashCode_(node);
+    var listenerHc = getHashCode_(listener);
+    opt_useCapture = !!opt_useCapture;
+    var key = nodeHc + '_' + event + '_' + listenerHc + '_' + opt_useCapture;
+    return key;
+  }
+
+  /**
+   * Adds an event listener to a DOM node for a specific event.
+   *
+   * Listen() and unlisten() use an indirect lookup of listener functions
+   * to avoid circular references between DOM (in IE) or XPCOM (in Mozilla)
+   * objects which leak memory. This makes it easier to write OO
+   * Javascript/DOM code.
+   *
+   * Examples:
+   * listen(myButton, 'click', myHandler, true);
+   * listen(myButton, 'click', this.myHandler.bind(this), true);
+   *
+   * @param {Element} node The node to listen to events on.
+   * @param {string} event The name of the event without the "on" prefix.
+   * @param {Function} listener A function to call when the event occurs.
+   * @param {boolean} opt_useCapture In DOM-compliant browsers, this determines
+   *                                 whether the listener is fired during the
+   *                                 capture or bubble phase of the event.
+   * @return {string} a unique key to indentify this listener.
+   */
+  listen = function(node, event, listener, opt_useCapture) {
+    var key = createKey_(node, event, listener, opt_useCapture);
+
+    // addEventListener does not allow multiple listeners
+    if (key in listeners) {
+      return key;
+    }
+
+    var proxy = handleEvent.bind(null, key);
+    listeners[key] = {
+      listener: listener,
+      proxy: proxy,
+      event: event,
+      node: node,
+      useCapture: opt_useCapture
+    };
+
+    if (node.addEventListener) {
+      node.addEventListener(event, proxy, opt_useCapture);
+    } else if (node.attachEvent) {
+      node.attachEvent('on' + event, proxy);
+    } else {
+      throw new Error('Node {' + node + '} does not support event listeners.');
+    }
+
+    return key;
+  }
+
+  /**
+   * Removes an event listener which was added with listen().
+   *
+   * @param {Element} node The node to stop listening to events on.
+   * @param {string} event The name of the event without the "on" prefix.
+   * @param {Function} listener The listener function to remove.
+   * @param {boolean} opt_useCapture In DOM-compliant browsers, this determines
+   *                                 whether the listener is fired during the
+   *                                 capture or bubble phase of the event.
+   * @return {boolean} indicating whether the listener was there to remove.
+   */
+  unlisten = function(node, event, listener, opt_useCapture) {
+    var key = createKey_(node, event, listener, opt_useCapture);
+
+    return unlistenByKey(key);
+  }
+
+  /**
+   * Variant of {@link unlisten} that takes a key that was returned by
+   * {@link listen} and removes that listener.
+   *
+   * @param {string} key Key of event to be unlistened.
+   * @return {boolean} indicating whether it was there to be removed.
+   */
+  unlistenByKey = function(key) {
+    if (!(key in listeners)) {
+      return false;
+    }
+    var listener = listeners[key];
+    var proxy = listener.proxy;
+    var event = listener.event;
+    var node = listener.node;
+    var useCapture = listener.useCapture;
+
+    if (node.removeEventListener) {
+      node.removeEventListener(event, proxy, useCapture);
+    } else if (node.detachEvent) {
+      node.detachEvent('on' + event, proxy);
+    }
+
+    delete listeners[key];
+    return true;
+  }
+
+  /**
+   * The function which is actually called when the DOM event occurs. This
+   * function is a proxy for the real listener the user specified.
+   */
+  function handleEvent(key) {
+    // pass all arguments which were sent to this function except listenerID
+    // on to the actual listener.
+    var args = Array.prototype.splice.call(arguments, 1, arguments.length);
+    return listeners[key].listener.apply(null, args);
+  }
+
+})();