Image aspect ratio from url

AspectRatioTest.coffee

@img = null
# Using an Image Object
getAspectRatio = (url, callback) ->
  @img = img = new Image()
  img.onload = ->
    callback null, @width/@height, @width, @height
  img.onerror = ->
    callback "Failed loading #{url}"
  img.src = url

turl = 'http://cdn.sstatic.net/stackoverflow/img/sprites.png?v=3c6263c3453b'
getAspectRatio turl, (err, ratio) ->
  Say(ratio or err)

getAspectRatio.js

(function () {
var getAspectRatio = function(url, callback) {
  var img = new Image();
  img.onload = function() {
    return callback(null, this.width / this.height, this.width, this.height);
  };
  img.onerror = function() {
    return callback("Failed loading " + url);
  };
  return img.src = url;
};
if (typeof module !== "undefined")
  module.exports = getAspectRatio;
else
  this.getAspectRatio = getAspectRatio;
})();