[kidmac]

on the server side.
get what the user entered, check if its valid, and then generate that line of html. For example in php, assuming it was a POST request:

<?php
    $input = $_POST['inputFieldName'];
    validateInput($input) or header("location: backtotheform.html"); // pseudo line
?>

<script type="text/javascript" src="http://domain.com/index.php?mode=js&zipcode=<?php echo $input; ?>"></script>

I have no idea how to do this help me plz