<script>
      window.onload=function(){
      	var login_btn=document.getElementById('login'),
      	    login_box=document.getElementById('login_box'),
      	    close=document.getElementById('close');
      	// 封装添加事件监听程序
        function addEvent(ele,type,hander){
           // 执行代码  
           if(ele.addEventListener){
               ele.addEventListener(type,hander,false);
           }
           else if(ele.attachEvent){
               ele.attachEvent("on"+type,hander);
           }
           else{
               ele.["on"+type]=hander;
           }
      	}
        // 显示登录层函数
      	function showLogin(){
            login_box.style.display="block";
        }
        // 隐藏登录层函数
        function hideLogin(){          
          login_box.style.display="none";
        }
        //点击登录按钮显示登录层         
        addEvent(login_btn,"click",showLogin);
        //点击关闭按钮隐藏登录层
        addEvent(close,"click",hideLogin);
      
	</script>