一、必填（或必选）项目
<script type="text/javascript">// <![CDATA[
function validate_required(field,alerttxt)
{
with(field)
if(value==null||value=="")
{
alert(alerttxt);return false
}
else
{
return true
}
}
function validate_form(thisfrom)
{
with(thisform)
if(validate_required(email,"Email must be filled out!")==false)
{email.focus;return false}
}
</script>
Email验证，输入的数据必须包含 @ 符号和点号(.)。同时，@ 不可以是邮件地址的首字符，并且 @ 之后需有至少一个点号：
<html>
<head>
<script type="text/javascript">
function validate_email(field,alerttxt)
{
with (field)
{
apos=value.indexOf("@")
dotpos=value.lastIndexOf(".")
if (apos<1||dotpos-apos<2)
{alert(alerttxt);return false}
else {return true}
}
}
function validate_form(thisform)
{
with (thisform)
{
if (validate_email(email,"Not a valid e-mail address!")==false)
{email.focus();return false}
}
}
</script>
</head>
<body>
<form action="submitpage.htm"onsubmit="return validate_form(this);" method="post">
Email: <input type="text" name="email" size="30">
<input type="submit" value="Submit">
</form>
</body>
</html>