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;
    }
};

//------------- 以下为测试代码 -----------

// 添加自定义事件
var fnAlert1, fnAlert2;
Event.addEvent("alert", fnAlert1 = function() {
    alert("第一个弹出！");
}).addEvent("alert", fnAlert2 = function() {
    alert("第二个弹出！");
});

// 按钮绑定事件，用来清除自定义事件
var elButton1 = document.getElementById("button1"),
    elButton2 = document.getElementById("button2");

elButton1.onclick = function() {
    Event.removeEvent("alert");
    alert("alert事件清除成功！");
    
    // 此时后一个按钮卧底了，故隐藏
    elButton2.style.display = "none";
};

elButton2.onclick = function() {
    Event.removeEvent("alert", fnAlert1);
    alert("第一个alert清除成功！");
};

// 点击文档，触发自定义事件
document.onclick = function(e) {
    e = e || window.event;
    var target = e.target || e.srcElement;
    
    // 如果文档点击元素标签名不是input
    if (!target || !/input|pre/i.test(target.tagName)) {
        Event.fireEvent("alert");
    }
};