<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
 <head>
  <title> new document </title>
  <meta http-equiv="Content-Type" content="text/html;charset=UTF-8" />
  <meta name="author" content="" />
  <meta name="keywords" content="" />
  <meta name="description" content="" />
  <link rel="stylesheet" type="text/css" href="" />
  <style type="text/css">
   .login{width:40px;height:25px;line-height:25px;background-color:#4E74A5;margin-top:30px;text-align:center;color:#FFF;}
  </style>
  <script type="text/javascript" src="jquery-1.7.1.min.js"></script>
 </head>
 <body onkeydown="keyLogin();">
  <input type="text" class="pass"  value="" />
  <div id="enter" class="login"  onclick="enter_login();"> 登录</div>

  <script type="text/javascript">
      function enter_login(){
        var pwd = $(".pass").val();
            if(pwd==""){
                alert(1);
            }else{
                alert(2);
            }
    }
      function keyLogin(){  
                if (event.keyCode==13){
                    document.getElementById("enter").click(); 
                }                                
            }  
  </script>
 </body>
</html>