SOURCE

var Event = {
    _listeners: {},    
    addEvent: function(type, fn) {
        if (typeof this._listeners[type] === "undefined") {
            this._listeners[type] = [];
        }
        if (typeof fn === "function") {
            this._listeners[type].push(fn);
        }    
        return this;
    },
    fireEvent: function(type) {
        var arrayEvent = this._listeners[type];
        if (arrayEvent instanceof Array) {
            for (var i=0, length=arrayEvent.length; i<length; i+=1) {
                if (typeof arrayEvent[i] === "function") {
                    arrayEvent[i]({
                        type: type    
                    });    
                }
            }
        }    
        return this;
    },
    removeEvent: function(type, fn) {
        var arrayEvent = this._listeners[type];
        if (typeof type === "string" && arrayEvent instanceof Array) {
            if (typeof fn === "function") {
                for (var i=0, length=arrayEvent.length; i<length; i+=1){
                    if (arrayEvent[i] === fn){
                        this._listeners[type].splice(i, 1);
                        break;
                    }
                }
            } else {
                delete this._listeners[type];
            }
        }
        return this;
    }
};

if (window.HTMLElement) {
    // 使用原型扩展DOM自定义事件
    
    HTMLElement.prototype.addEvent = function(type, fn, capture) {
        var el = this;
        if (window.addEventListener) {
            el.addEventListener(type, function(e) {
                fn.call(el, e);
            }, capture);
        } else if (window.attachEvent) {
            el.attachEvent("on" + type, function(e) {
                fn.call(el, e);
            });
        } 
    };
} else {
    // 如果是不支持HTMLElement扩展的浏览器
    // 通过遍历所有元素扩展DOM事件
    
    var elAll = document.all, lenAll = elAll.length;
    for (var iAll=0; iAll<lenAll; iAll+=1) {
        elAll[iAll].addEvent = function(type, fn) {
            var el = this;
            el.attachEvent("on" + type, function(e) {
                fn.call(el, e);
            });
        };
    }
    
}