纯js事件注册方法（解决兼容性）

var addEvent = (function() {
    if (document.addEventListener) {
        return function(el, type, fn) {
            if (el.length) {
                for (var i = 0; i < el.length; i++) {
                    addEvent(el[i], type, fn);
                }
            } else {
                el.addEventListener(type, fn, false);
            }
        };
    } else {
        return function(el, type, fn) {
            if (el.length) {
                for (var i = 0; i < el.length; i++) {
                    addEvent(el[i], type, fn);
                }
            } else {
                el.attachEvent('on' + type,
                function() {
                    return fn.call(el, window.event);
                });
            }
        };
    }
})();