Added a EventWindow class

app/js/ui/EventWindow.js

+import '/app/js/EventCaller.js'
+
+/**
+ *  Wraps the browser's window object around the EventCaller allowing the user to connect to system events
+ *  by listening for those events (ex: "onclick", "onresize", etc).
+ *
+ *  Users should not directly set the window event handler functions if using this class.
+ */
+export class EventWindow extends EventCaller{
+  constructor(){
+    super();
+  }
+
+  listen(eventName, callback, owner=null, once=false){
+    if (window.hasOwnProperty(eventName)){
+      if (window[eventName] === null || typeof(window[eventName]) === 'undefined'){
+        window[eventName] = (function(event){
+          this.emit(eventName, event);
+        }).bind(this);
+      }
+      super.listen(eventName, callback, owner, once);
+      return this;
+    }
+    throw new ValueError("Window object has no event named '" + eventName +"'.");
+  }
+
+  unlisten(eventName, callback, owner=null){
+    if (window.hasOwnProperty(eventName)){
+      super.unlisten(eventName, callback, owner);
+      if (super.event_listener_count(eventName) == 0){
+        window[eventName] = undefined;
+      }
+    }
+    return this;
+  }
+
+  unlisten_event(eventName){
+    if (window.hasOwnProperty(eventName)){
+      super.unlisten_event(eventName);
+      window[eventName] = undefined;
+    }
+    return this;
+  }
+
+  unlisten_all(){
+    var we = this.watchedEvents;
+    super.unlisten_all();
+    for (var i=0; i < we.length; i++){
+      if (window.hasOwnProperty(we[i])){
+        window[we[i]] = undefined;
+      }
+    }
+    return this;
+  }
+}