Does anyone know how to pass values from a popup window back to parent window?

I'm trying to make a username verification of whether the entered username already exists in my database.

I used document.getElementById plus window.open to pass the entered username to a popup window that is a php file. I can do the MySQL connection and checking there but I need to return something from the popup window back to the parent window so that I can stop form submission if the username already exists.

Any help would be appreicated.

Try using a cookie.

Thanks, however I found a way myself.
using opener.document.(whatever after)=(whatever value);

You know if your using PHP (More Secure) you could create a session.

yeah Javascript works if you are noty sending sensitive inbfo that you can later view in the address bar but I like window.opener

can everybody help me ho to pass values from popup window to text on parent window.i want coding in php..