Check Pending AJAX requests or HTTP GET/POST request
I see you mention you are using Prototype.js. You can track active requests with Prototype by checking the Ajax.activeRequestCount value. You could check this using setTimeout or setInterval to make sure that any requests triggered on page load have completed (if that's what you're looking to do)
How do i check if the page has pending AJAX or HTTP GET/POST requests? I use javascript and/or python for this checking. 
what i wanted to do is execute a script if a page has finished all requests. onload doesn't work for me, if you used firebugs net panel, you would know. onload fires when the page is loaded but there is a possibility that there are still pending request hanging around somewhere.
thank you in advance.