Javascript Helper to turn easy to load a polyfill library just if necessary

check-load-polyfills.js

/*

Usage Example:
window.PolyfillHelpers.loadPolyfillLib(
  // Callback condition that says if the polyfill need to be loaded or not
  function () { return ('Promise' in window); },
  // Polyfill lib path
  '/bower_components/es6-promise/es6-promise.auto.min.js', { async: false },
  // Polyfill check/load completed
  function(polyfillUsed) {
    console.log('[PolyfillHelpers.loadPolyfillLib][Promise]->polyfillUsed: ', polyfillUsed);
  }
);

*/
window.PolyfillHelpers = window.PolyfillHelpers || {};
;(function(PolyfillHelpers) {
  PolyfillHelpers.loadPolyfillLib = function (checkCallback, polyfillPath, opt, onload) {
    if (checkCallback) { 
      opt = opt || {};
      opt.async = (opt.async === undefined) ? true : opt.async;  
      
      var cbResult = checkCallback();

      if (!cbResult) {
        var script = document.createElement('script');
        script.async = opt.async;
        script.src = polyfillPath;
        script.onload = function () { 
          onload(true); /* param: polyfillUsed */
        };
        document.head.appendChild(script);
      } else {
        onload(false);
      }
    }
  };
}(window.PolyfillHelpers));