<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(){
              // 执行代码
            login_box.style.display = "block";  
        }
        // 隐藏登录层函数
        function hideLogin(){
          // 执行代码
          login_box.style.display = "none";
        }
        //点击登录按钮显示登录层
        // 执行代码
         addEvent(login_btn,"click",showLogin);
        //点击关闭按钮隐藏登录层
        // 执行代码
        addEvent(close,"click",hideLogin);
      }
    </script>