hello everyone i have a idea for making web app AJAX Based that need periodic request. i'am so sorry coz i'am not implementing this idea yet.

my idea is making web app for uploading file with progress bar indicator. so., the file that i have to upload with iframe technique. and i will make one script again again that checking file on the server. so.., i / the script need to listening continuesly to the file on the server.

how i can implement this periodic request ??