* { margin: 0; padding: 0; }

 var  helper = {}

 //绑定事件
 helper.on = function(target, type, handler) {
 	if(target.addEventListener) {
 		target.addEventListener(type, handler, false);
 	} else {
 		target.attachEvent("on" + type,
 			function(event) {
 				return handler.call(target, event);
 		    }, false);
 	}
 };

 //取消事件监听
 helper.remove = function(target, type, handler) {
 	if(target.removeEventListener) {
 		target.removeEventListener(type, handler);
 	} else {
 		target.detachEvent("on" + type,
 	    function(event) {
 			return handler.call(target, event);
 		}, true);
     }
 };

var scrollTop = document.documentElement.scrollTop||document.body.scrollTop;

<!--[if IE 8]> ie8 <![endif]-->
 
 <!--[if IE 9]> 骚气的 ie9 浏览器 <![endif]-->

/* Safari */
 var isSafari = /a/.__proto__=='//';

/* Chrome */
 var isChrome = Boolean(window.chrome);