Javascript - Jquery Postal Code Clientvalidate?

I am working on a customvalidator to validate and replace (if possible) a postal code.

This is a Dutch postal code and should look like "5050 AA". When the user enters "5050AA" this postal code should be replaced with "5050 AA". I tried this by adding the following script to my page, which is called in the customvalidator:

<script type="text/javascript">
function Postcode_ClientValidate(source, arguments) {
var val = arguments.Value
var result = "";
var myPCRegExp1 = new RegExp("^[1-9][0-9]{3}s?[a-zA-Z]{2}$", "i");

[code]....

However, the script above is picking up the "5038AA" but not the "5038 AA" as a match, so i can't validate a working postal code and can't rewrite to the valid postal code.