Window width bookmarklet

javascript:(function() {

  var d = document,
      w = window,
      sw = function() { return Math.max(d.documentElement.clientWidth, w.innerWidth) },
      i = d.createElement("div"),
      s = "position:fixed;top:0;right:0;padding:4px 6px;z-index:999999;opacity:.8;background:#000;color:#fff;font:15px HelveticaNeue";

  i.setAttribute("style", s);
  i.innerHTML = sw() + "px";
  d.querySelector("body").appendChild(i);

  if (w.addEventListener)
    w.addEventListener("resize", function() { go(sw) });
  else if (w.attachEvent)
    w.attachEvent("onresize", function() { go(sw) });
  else 
    w.onresize = function() { go(sw) };

  function go() {
    i.innerHTML = sw() + "px";
  }

}());