Window closed Property

function checkWin() {
    if (!myWindow) {
        document.getElementById("msg").innerHTML = "'myWindow' has never been opened!";
    } else {
          if (myWindow.closed) {
              document.getElementById("msg").innerHTML = "'myWindow' has been closed!";
          } else {
              document.getElementById("msg").innerHTML = "'myWindow' has not been closed!";
          }
    }
}