登陆界面的验证代码

<script language="javascript">
<!--
function CheckForm()
{
if (document.Form1.txtusername.value =="") {
alert("用户名不能为空！");
document.Form1.txtusername.focus();
return false;
}
if (document.Form1.txtpwd.value == ""){
alert("密码不能为空！");
document.Form1.txtpwd.focus();
return false;
}
if (document.Form1.txtcode.value == ""){
alert("请输入验证码！");
document.Form1.txtcode.focus();
return false;
}
return true;
}
function clsInput()
{
document.Form1.txtusername.value =""
document.Form1.txtpwd.value= ""
document.Form1.txtcode.value= ""
return true;
}

//-->
</script>