Javascript - Close Child Aspx Page If Gridview Index Is Changed On Parent Page?

I have a parent page and child page, both aspx. All is working, but now I would like to close child page, if user leaves child popup page and goes back to parent page and clicks on something else like page index of Gridview. I CANNOT close popup child page if user goes to another app, or some other location, I only want to close if something on parent page is changed.

I have the PageIndexChange Event set up for other purposes, I would just like to add some functionality, perhaps a script manager to close the child popup page if the Gridview index is changed, java or another way which ever works best.I think I might also need to check if the child page is even open.

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