function loginInput()
{
  var txtUserName=document.getElementById("txtUserName").value; 
  var txtpwd=document.getElementById("txtPwd").value; 
  if(txtUserName=="")
  {
     alert("请输入用户名");
     document.getElementById("txtUserName").focus();
     return false;
  }
  if(txtpwd=="")
  {
     alert("请输入密码");
     document.getElementById("txtPwd").focus();
     return false;
  }
}