if (navigator.userAgent.match(/iPhone/i) || navigator.userAgent.match(/iPad/i)) {
  var viewportmeta = document.querySelectorAll('meta[name="viewport"]')[0];
  if (viewportmeta) {
    viewportmeta.content = 'width=device-width, minimum-scale=1.0, maximum-scale=1.0';
    document.body.addEventListener('gesturestart', function() {
      viewportmeta.content = 'width=device-width, minimum-scale=0.25, maximum-scale=1.6';
    }, false);
  }
}