function reloadWin() {
  if (!win.closed) win.location.reload();
}

var win = open("test.html");
setTimeout("reloadWin()", 60000); // reload after one minute

When a window closes, the window object that represents it continues to exist, and its closed property is set to true. Use closed to determine whether a window that you opened, and to which you still hold a reference (from the return value of the window.open() method), is still open. Once a window is closed, you should not attempt to manipulate it, or you will receive a nasty JavaScript error.

For more information, refer to the official documentation from Microsoft and Netscape.

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