Jiang-Xuan · January 30, 2018 02:46 · Jan 30, 2018
diff --git a/dom2EventTarget.js b/dom2EventTarget.js
@@ -0,0 +1,60 @@
+/* Simplified implementation of DOM2 EventTarget.
+ *   http://www.w3.org/TR/DOM-Level-2-Events/events.html#Events-EventTarget
+ */
+
+function EventTarget() {
+  this._listeners = {};
+}
+
+EventTarget.prototype.addEventListener = function(eventType, listener) {
+  if (!(eventType in this._listeners)) {
+    this._listeners[eventType] = [];
+  }
+  var arr = this._listeners[eventType];
+  // #4
+  if (arr.indexOf(listener) === -1) {
+    // Make a copy so as not to interfere with a current dispatchEvent.
+    arr = arr.concat([listener]);
+  }
+  this._listeners[eventType] = arr;
+};
+
+EventTarget.prototype.removeEventListener = function(eventType, listener) {
+  var arr = this._listeners[eventType];
+  if (!arr) {
+    return;
+  }
+  var idx = arr.indexOf(listener);
+  if (idx !== -1) {
+    if (arr.length > 1) {
+      // Make a copy so as not to interfere with a current dispatchEvent.
+      this._listeners[eventType] = arr.slice(0, idx).concat(arr.slice(idx + 1));
+    } else {
+      delete this._listeners[eventType];
+    }
+    return;
+  }
+};
+
+EventTarget.prototype.dispatchEvent = function() {
+  var event = arguments[0];
+  var t = event.type;
+  // equivalent of Array.prototype.slice.call(arguments, 0);
+  var args = arguments.length === 1 ? [event] : Array.apply(null, arguments);
+  // TODO: This doesn't match the real behavior; per spec, onfoo get
+  // their place in line from the /first/ time they're set from
+  // non-null. Although WebKit bumps it to the end every time it's
+  // set.
+  if (this['on' + t]) {
+    this['on' + t].apply(this, args);
+  }
+  if (t in this._listeners) {
+    // Grab a reference to the listeners list. removeEventListener may alter the list.
+    var listeners = this._listeners[t];
+    for (var i = 0; i < listeners.length; i++) {
+      listeners[i].apply(this, args);
+    }
+  }
+};
+
+module.exports = EventTarget;