var newWindow = null;

function opencsWindow() {
         newWindow = window.open("contractenset.html", "newwindow", "height=450,width=780,scrollbars=yes,resizable=yes,screenX=50,screenY=50");
         newWindow.focus()
}

function closeWindow() {
      if (newWindow != null) {
          newWindow.close();
          newWindow = null;
      }
}