function checkval(){
 	if (form1.username.value==""){
		  alert("请输入用户名！");
		  form1.username.focus();
		  return false;
	  }
	if (form1.password.value==""){
		  alert("请输入密码");
		  form1.password.focus();
		  return false;
	  }
   if(form1.code.value.length!=4){
	  alert("请正确输入4位的验证码");
	  form1.code.focus();
	  return false;
   }
}