Very simple reduction of PictureFill.js - not suitable for production

picturefill.ultralight.js

// var retina = window.devicePixelRatio > 1;
var retina = window.devicePixelRatio > 1;

if (retina) {
    // the user has a retina display

    // tbh - lets just drop a cookie, and handle this stuff server-side
    // document.cookie='HTTP_IS_RETINA=1;path=/'

    $(function ()  {

      var images = document.getElementsByTagName("img");
      matches = [];


     for (var j = 0, jl = images.length; j < jl; j++) {
          var media = images[j].getAttribute("data-retina-src");
          if (media) { 
            console.log(images[j]);
            images[j].src = media;
          }
        }
      
    });
  
}
else {
    // the user has a non-retina display
}