Javascript Example
Screen shot
Javascript code for form validation with alert
<html>
<head>
<title>Javascript Form Validation with Alert</title>
<script language=\"javascript\">
function validate()
{
msg = \"Please fill the following information:\\n\\n\";
str = \"\";

if(document.frm.userid.value==\'\')
{
str+=\"-Please Insert User ID\\n\";
}

if(document.frm.password.value==\'\')
{
str+=\"-Please Insert Password\\n\";
}

if(document.frm.password.value!=document.frm.confirm_password.value)
{
str+=\"-Password and Confirm Password does not Match\\n\";
}

var validate_char= /^[\\w\\-\\.\\+]+\\@[a-zA-Z0-9\\.\\-]+\\.[a-zA-z0-9]{2,4}$/;
if(!document.frm.email.value.match(validate_char))
{
str+=\'-Please enter a valid email address\\n\';
}

if(str)
{
alert(msg+str);
return false;
}
else
{
return true;
}

}
</script>
</head>
<body>
<form name=\"frm\" action=\"\" method=\"post\" onSubmit=\"return validate()\">
<table border=\"1\" align=\"center\">
<tr>
<td>User ID</td>
<td><input name=\"userid\" type=\"text\"></td>
</tr>
<tr>
<td>Password</td>
<td><input name=\"password\" type=\"password\"></td>
</tr>
<tr>
<td>Confirm Password</td>
<td><input name=\"confirm_password\" type=\"password\"></td>
</tr>
<tr>
<td>Email</td>
<td><input name=\"email\" type=\"text\"></td>
</tr>
<tr>
<td colspan=\"2\" align=\"center\">
<input name=\"btnsubmit\" type=\"submit\" value=\"Submit\">
</td>
</tr>
</table>
</form>
</body>
</html>

You can download source code here