Showing a default image if an image doesn't exist in jQuery

default_image.js

var img = $('img');
var default_url = "http://example.org/images/img.jpg";
var img_url = "http://example.org/images/" + some_variable + ".jpg";
img.error(function() {
  $(this).attr('src', default_url) 
});
img.attr('src', img_url);