How to run function of parent window when child window closes?

Question

I am calling the javascript window.open() function to load another url in a pop up. Once the users is finished it takes them to the last page that has a link that says close

Answer 1

The answers as they are require you to add code to the spawned window. That is unnecessary coupling.

// In parent window
var pop = open(url);
pop.onunload = function() {
  // Run your code, the popup window is unloading
  // Beware though, this will also fire if the user navigates to a different
  // page within thepopup. If you need to support that, you will have to play around
  // with pop.closed and setTimeouts
}