How to determine whether to open a window

Using the window.closed; property can detect the current window is closed, since the code is run in this window, so long run, it shows that this is not closed and therefore the properties used for detecting the created to window.open (). the window is closed;

var A = the window.open ();
 IF (! A == null ! && a.closed) { 
    the console.log ( "A window is not closed" ); 
}