The opener property of the window object provides access to the window object that opened the current window.

To see this in action create 2 new html files. Name one file "main_doc.html", and the other "other_doc.html". We are going to make the main document pop open the other document, then once the other document is opened it will instruct the main opener window to head to a new location that we specify.

main_doc.html

other_doc.html