js以类似jquery的模式绑定事件

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>

<body>
    <button class="a"></button>
</body>

</html>
<script>
    var $ = function (el) {
        return new _$(el);
    };
    var _$ = function (el) {
        this.el = (el && el.nodeType == 1) ? el : document;
    };
    _$.prototype = {
        constructor: _$,
        addEvent: function (type, fn, capture) {
            var el = this.el;

            if (window.addEventListener) {
                el.addEventListener(type, fn, capture);

                var ev = document.createEvent("HTMLEvents");
                ev.initEvent(type, capture || false, false);
                // 在元素上存储创建的事件，方便自定义触发
                if (!el["ev" + type]) {
                    el["ev" + type] = ev;
                }

            } else if (window.attachEvent) {
                el.attachEvent("on" + type, fn);
                if (isNaN(el["cu" + type])) {
                    // 自定义属性，触发事件用
                    el["cu" + type] = 0;
                }

                var fnEv = function (event) {
                    if (event.propertyName == "cu" + type) {
                        fn.call(el);
                    }
                };

                el.attachEvent("onpropertychange", fnEv);

                // 在元素上存储绑定的propertychange事件，方便删除
                if (!el["ev" + type]) {
                    el["ev" + type] = [fnEv];
                } else {
                    el["ev" + type].push(fnEv);
                }
            }

            return this;
        },
        fireEvent: function (type) {
            var el = this.el;
            if (typeof type === "string") {
                if (document.dispatchEvent) {
                    if (el["ev" + type]) {
                        el.dispatchEvent(el["ev" + type]);
                    }
                } else if (document.attachEvent) {
                    // 改变对应自定义属性，触发自定义事件
                    el["cu" + type]++;
                }
            }
            return this;
        },
        removeEvent: function (type, fn, capture) {
            var el = this.el;
            if (window.removeEventListener) {
                el.removeEventListener(type, fn, capture || false);
            } else if (document.attachEvent) {
                el.detachEvent("on" + type, fn);
                var arrEv = el["ev" + type];
                if (arrEv instanceof Array) {
                    for (var i = 0; i < arrEv.length; i += 1) {
                        // 删除该方法名下所有绑定的propertychange事件
                        el.detachEvent("onpropertychange", arrEv[i]);
                    }
                }
            }
            return this;
        }
    };

    var dom = document.querySelector(".a");
    var test = $(dom).addEvent("alert", function () {
        alert("弹弹弹，弹走鱼尾纹~~");
    }, false);

test.fireEvent("alert");
</script>