function click (e) {
    if (!e) {
      e = window.event;
    }
    if ((e.type && e.type == "contextmenu") || (e.button && e.button == 2) || (e.which && e.which == 3)) {
      alert('No rightclick allowed.');
      return false;
    }
  }
  document.oncontextmenu = click;