var metas = document.getElementsByTagName('meta');

  var i;

  if (navigator.userAgent.match(/iP(hone|ad)/i)) {
    for (i=0; i<metas.length; i++) {
      if (metas[i].name == "viewport") {
        metas[i].content = "width=device-width, minimum-scale=1.0, maximum-scale=1.0";
      }
    }
    document.addEventListener("gesturestart", gestureStart, false);
  }

  function gestureStart() {
    for (i=0; i<metas.length; i++) {
      if (metas[i].name == "viewport") {
        metas[i].content = "width=device-width, minimum-scale=0.25, maximum-scale=1.6";
      }
    }
  }