var WindowObjectReference = null; // global variable

function carte(ville, width, height) {

  if (WindowObjectReference == null || WindowObjectReference.closed) {
 
  /* if the pointer to the window object in memory does not exist
     or if such pointer exists but the window was closed */

    WindowObjectReference = window.open("../carte/" +ville+".htm", ville, "scrollbars=yes,status=no,width="+width+",height="+height);
    /* then create it. The new window will be created and
       will be brought on top of any other window. */
  }
  else {
    WindowObjectReference.focus();
    /* else the window reference must exist and the window
       is not closed; therefore, we can bring it back on top of any other
       window with the focus() method. There would be no need to re-create
       the window or to reload the referenced resource. */
  };
}