Calling a function of the opener window

Using JavaScript, you can call a function in the opener window: the window that opened the current window by calling window.open. Here is the code:

if (window.opener) {
  window.close();
  window.opener.foo("bar");
}

First, it checks whether the opener window is still open. If it is, the code closes the current window and calls the foo function in the opener window.