js验证登录

<script language="javascript" type="text/javascript">
//获取用户名和密码

var usetname  = document.getElementById("username").value;

var password = document.getElementById("password").value;

function check(){

  if(username.value == ""){

alert("请输入用户名!");

document.getElementById("username").focus();

return false;

}

 if (password == "") {
  alert('请输入您的密码...');

document.getElementById("password").focus();

    return false;
  }

return true;

}

 

</script>