Sending values back to opener from user control

I have this window(popup) that gets opened from a another window(original). On the popup I have a user control. After the user finishes with the form I would like the values from the usercontrol on the popup to be sent back to the original window.

But I have no idea how to do it. The javascript that I have to do this from form to form is this:

window.opener.document.forms[0].txtFieldName.value = document.forms[0].FieldName.value;

and it works, but not from user control to form which is what i want to fix.

I also noticed to to get things to work on the user control from page_load of the form that it sits on is something like this:

Page.RegisterHiddenField("__EVENTTARGET", "UserControl1:btnSearch")

Where I have to have the name of the usercontrol and then : and then the name of the control.

Can someone please help me with this please.

Thanks again.

Nevermind, I fixed my own problem.

When I looked in the source of the page the id for the controls was:

UserControl1_txtFieldName

So i tried this before in the line of code i had before, but i guess that I forgot that javascript is case sensitive, so it works fine now.

Thanks anyways.