Retina.js

var Retina = Retina || {};
 
Retina = {
  init: function() {
    var images = document.querySelectorAll("img[data-1x]");
    var attr   = Retina.isRetina() ? "data-2x" : "data-1x";
    
    Array.prototype.forEach.call(images, function(el, i) {
      var src = el.getAttribute(attr);
      el.setAttribute("src", src);
    });    
  },
 
  isRetina: function() {
    return window.devicePixelRatio == 2;
  }
};