handlebars.retina.js

/*
 * Retina Images using Handlebars.js
 *
 * Created by [Makis Tracend](@tracend)
 * Released under the [MIT license](http://makesites.org/licenses/MIT) 
 *
 * Usage: <img src="{{retina 'http://mydoma.in/path/to/image.jpg'}}">
 */
Handlebars.registerHelper('retina', function( src ) {
  
  // first check if it's a retina screen
  var retina_screen = (typeof window === 'undefined') 
    ? /iPad/.test( request.headers['user-agent'] ) // server-side monitoring currently limited to iPad, based on the user-agent
    : ( window.devicePixelRatio > 1 );
    
  // output relevant image source 
  return ( retina_screen ) 
    ? src.replace(/\.\w+$/, function(match) { return "_x2" + match; }) 
    : src;
  
});