Slightly optimized version of the ‘Device Scale UI elements in iOS Mobile Safari’ script by 37signals

Slightly optimized version of the ‘Device Scale UI elements in iOS Mobile Safari’ script by 37signals

// Provides a device_scale class on iOS devices for scaling user
// interface elements relative to the current zoom factor.
//
// http://37signals.com/svn/posts/2407-device-scale-user-interface-elements-in-ios-mobile-safari
// Copyright (c) 2010 37signals.
// Slightly optimized by Mathias Bynens <http://mathiasbynens.be/>
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
// 
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

(function(d, w) {

 if (!('createTouch' in d)) return;

 var headElement = d.head || d.getElementsByTagName('head')[0],
     styleElement = d.createElement('style'),
     stylesheet;

 headElement.appendChild(styleElement);

 stylesheet = styleElement.sheet;

 w.addEventListener('scroll', updateDeviceScaleStyle, false);
 w.addEventListener('resize', updateDeviceScaleStyle, false);
 w.addEventListener('load', updateDeviceScaleStyle, false);
 updateDeviceScaleStyle();

 function updateDeviceScaleStyle() {
  if (stylesheet.rules.length) {
   stylesheet.deleteRule(0);
  };
  stylesheet.insertRule('.device-scale {-webkit-transform:scale(' + getDeviceScale() + ')}', 0);
 };

 // Adapted from code by Mislav Marohnić: http://gist.github.com/355625
 function getDeviceScale() {
  var landscape = Math.abs(window.orientation) === 90,
      deviceWidth = landscape ? Math.max(480, screen.height) : screen.width; // iPhone OS < 3.2 reports a screen height of 396px
  return w.innerWidth / deviceWidth;
 };

})(document, window);