modernizr_async-1.js

(function() {
  var modernizr = document.createElement('script');
  modernizr.type = 'text/javascript';
  modernizr.async = true;
  modernizr.src = '//cdn.example.com/Modernizr/applicationcache-cssclasses-history-localstorage-shiv.js';
  var s = document.getElementsByTagName('script')[0];
  s.parentNode.insertBefore(modernizr, s);
})();

use_callback.js

var _modernizr = [
  ['history', function(){
    /* 'history' is present or polyfill loaded */
  }],
  function(){
    /* last callback: all features present or polyfills loaded */
  }
];