AJAX - The Complete Reference

388 Part II: Developing an Ajax Library^

In PHP, it is possible to write a simple script to check format validity of a passed ZIP value:

<?php

header("Cache-Control: no-cache");

header("Pragma: no-cache");

$zip = htmlentities(substr(urldecode($_GET['zip']),0,16));

if (preg_match("/(^\d{5}$)|(^\d{5}-\d{4}$)/", $zip))

print "valid";

else

print "notvalid";

?>

Then Ajax can be used to make a call to this PHP script and provide error messages. Of

course, there really is no reason to go to the network all the time for such a simple check.

This makes Ajax nearly as inefficient as its form-posting predecessor, as shown in Figure 8-13,

which shows numerous round trips during a user session.

Now, it would be easy enough to perform the kind of format validation that was

performed server side in client-side JavaScript. We hope readers already use this kind of

FIGURE 8-13 Ajax isn’t appropriate for every task