自定义事件

//自定义事件
 function EventTarget() {
     this.handlers = {};
 }
 EventTarget.prototype = {
     constructor: EventTarget,
     //注册
     addHandler: function(type, handler) {
         if (typeof this.handlers[type] == "undefined") {
             this.handlers[type] = [];
         }
         this.handlers[type].push(handler);
     },
     //触发
     fire: function(event) {
         if (!event.target) {
             event.target = this;
         }
         if (this.handlers[event.type] instanceof Array) {
             var handlers = this.handlers[event.type];
             for (var i = 0, len = handlers.length; i < len; i++) {
                 handlers[i](event);
             }
         }
     },
     //注销
     removeHandler: function(type, handler) {
         if (this.handlers[type] instanceof Array) {
             var handlers = this.handlers[type];
             for (var i = 0, len = handlers.length; i < len; i++) {
                 if (handlers[i] === handler) {
                     break;
                 }
             }
             handlers.splice(i, 1);
         }
     }
 };

//使用方法
 function handleMessage(event) {
     alert("Message received: " + event.message);
 }
 //创建一个新对象
 var target = new EventTarget();
 //添加一个事件处理程序
 target.addHandler("message", handleMessage);
 //触发事件
 target.fire({
     type: "message",
     message: "Hello world!"
 });
 //删除事件处理程序
 target.removeHandler("message", handleMessage);
 //再次，应没有处理程序
 target.fire({
     type: "message",
     message: "Hello world!"
 });