retina.js

// This will grab the largest image for the pixelRatio without oversampling (iOS style)
// Usage: assetUsingNativePixelRatio('/assets/images', 'logo', 'png', [1,2,3]);
// Output: /assets/images/logo@2x.png
function assetUsingNativePixelRatio(path, name, extension, pixelRatios) {
  
  // Sort the pixelRatios in case they were put in the wrong order
  var $pixelRatios = $(pixelRatios).sort();
  
  // Price is right style
  var matchingPixelRatio = $pixelRatios.not(function() {
    return (this > window.devicePixelRatio);
  }).last()[0];

  // Append everything together but if the pixel ratio is 1x don't put an "@1x" that's just silly
  return (path + '/' + name + (matchingPixelRatio > 1 ? ('@' + matchingPixelRatio + 'x') : '') + '.' + extension);

}