Added built-in noVNC support.

public/novnc/core/util/eventtarget.js

@@ -0,0 +1,35 @@
+/*
+ * noVNC: HTML5 VNC client
+ * Copyright (C) 2018 The noVNC Authors
+ * Licensed under MPL 2.0 (see LICENSE.txt)
+ *
+ * See README.md for usage and integration instructions.
+ */
+
+export default class EventTargetMixin {
+    constructor() {
+        this._listeners = new Map();
+    }
+
+    addEventListener(type, callback) {
+        if (!this._listeners.has(type)) {
+            this._listeners.set(type, new Set());
+        }
+        this._listeners.get(type).add(callback);
+    }
+
+    removeEventListener(type, callback) {
+        if (this._listeners.has(type)) {
+            this._listeners.get(type).delete(callback);
+        }
+    }
+
+    dispatchEvent(event) {
+        if (!this._listeners.has(event.type)) {
+            return true;
+        }
+        this._listeners.get(event.type)
+            .forEach(callback => callback.call(this, event));
+        return !event.defaultPrevented;
+    }
+}