This is a JQuery plugin that implements a way to observe form fields on a given frequency, instead of having to rely on blur (too cumberstone for the user) or keyup (too many server requests).
The frequency has to be specified in seconds.
Each onkeyup event resets the counter, so a frequency of more than 2 seconds will result on a not very responsive interface.
Make sure that JQuery is included before this plugin. Then include this file too.
Assuming that you copied it on /javascripts/:
<script src="/javascripts/jquery.observe_field.js" type="text/javascript"></script>
See example.html