一个支持优先级的自定义事件系统

在AS3中有一个叫IEventDispatcher 的类，与浏览器的window对象，document或元素节点一样，提供了 addEventListener, removeEventListener, dispatchEvent等接口。相对于浏览器的addEventListener，Flash的参数是更丰富，其中有一个允许我们指定回调的优先级，让我们在fire时优先执行它们。这是一个非常好的东西，JS想实现它也不能，于是便有以下这个类。以后，你想你的其他组件拥有自定义事件功能，那么继承它就行了。

以下是源码，使用AMD的形式包装。你们用时，可以使用我的加载器或requireJS加载它就行了。或者干脆把它的外层去掉！

define("events", function(){
    //与node.js events模块同名，返回EventTarget类
    var EventTarget = function(target) {
        this._listeners = {};
        this._eventTarget = target || this;
    }
    EventTarget.prototype = {
        constructor: EventTarget,
        addEventListener: function(type, callback, scope, priority) {
            if(isFinite( scope )){
                priority = scope
                scope = null;
            }
            priority = priority || 0;
            var list = this._listeners[type],  index = 0, listener, i;
            if (list == null) {
                this._listeners[type] = list = [];
            }
            i = list.length;
            while (--i > -1) {
                listener = list[i];
                if (listener.callback === callback) {
                    list.splice(i, 1);
                } else if (index === 0 && listener.priority < priority) {
                    index = i + 1;
                }
            }
            list.splice(index, 0, {
                callback: callback, 
                scope:    scope, 
                priority: priority
            });
        },
        removeEventListener: function(type, callback) {
            var list = this._listeners[type], i;
            if (list) {
                i = list.length;
                while (--i > -1) {
                    if (list[i].callback === callback) {
                        list.splice(i, 1);
                        return;
                    }
                }
            }
        },
        dispatchEvent: function(type) {
            var list = this._listeners[type];
            if (list) {
                var target = this._eventTarget,  args = Array.apply([], arguments),i = list.length,  listener
                while (--i > -1) {
                    listener = list[i];
                    target = listener.scope || target;
                    args[ 0 ] = {
                        type:  type,
                        target: target
                    }
                    listener.callback.apply(target, args);
                }
            }
        }
    }
    return EventTarget;
}) 

<!DOCTYPE HTML>
<html>
    <head>
        <title>EventTarget by 司徒正美</title>
        <meta http-equiv="Content-type" content="text/html; charset=utf-8">
        <script src="https://files.cnblogs.com/rubylouvre/mass.js">  </script>
        <script>
            require("events, mass", function(EventTarget, $){
                var a = new EventTarget;
                a.addEventListener("click", function(e){
                    $.log(e,true)
                })
                a.addEventListener("click", function(e){
                    $.log("高优先级",true)
                }, 2)
                a.addEventListener("click", function(e){
                    $.log("这是第三个回调",true)
                });
                a.addEventListener("click", function(e, a, b, c){
                    $.log(a, true)
                    $.log(b, true)
                    $.log(c, true)
                });
                a.dispatchEvent("click",1,2,3)
            })
        </script>
        <style>

</style>
    </head>
    <body>
     出错就刷新页面！

</body>
</html>

现在我把它放到github中，一切以github的为准！