提高js性能方法(让js只判断一次)

  来自我的javascript群

  方法一

var addEvent = (function () {
    if (document.addEventListener) {
        return function (el, type, fn) {
            el.addEventListener(type, fn, false);
        };
    } else {
        return function (el, type, fn) {
            el.attachEvent('on' + type, function () {
                return fn.call(el, window.event);
            });
        }
    }
})();

方法二

var addEvent = window.addEventListener ? function(el, type, fn) { el.addEventListener(type, fn, false); } : function(el, type, fn) { el.attachEvent('on' + type, fn); }