//事件派发机制的实现
var EventDispatcher = {
    addEventListener: function(eventType, handler){
        //事件的存储
        if(!this.eventMap){
            this.eventMap = {}
        }

        //对每个事件，允许添加多个监听
        if(!this.eventMap[eventType]){
            this.eventMap[eventType] = []
        }

        //把回调函数放入事件的执行数组
        this.eventMap[eventType].push(handler)
    },

    removeEventListener: function(eventType, handler){
        for(var i = 0; i < this.eventMap[eventType].length; i ++){
            if(this.eventMap[eventType][i] == handler){
                this.eventMap[eventType].spile(i, 1)
                break
            }
        }
    },

    dispatchEvent: function(event){
        var eventType = event.type;
        if(this.eventType && this.eventMap[eventType]){
            for(var i = 0; i < this.eventMap[eventType].length; i ++){
                //把对当前事件添加的处理函数拿出来挨个执行
                this.eventMap[eventType][i](event)
            }
        }
    }
}