open-wc/packages/polyfills-loader/test-node/snapshots/create-polyfills-loader/module-legacy-system.js

(function () {
  function loadScript(src, type) {
    return new Promise(function (resolve) {
      var script = document.createElement('script');

      function onLoaded() {
        if (script.parentElement) {
          script.parentElement.removeChild(script);
        }

        resolve();
      }

      script.src = src;
      script.onload = onLoaded;

      script.onerror = function () {
        console.error('[polyfills-loader] failed to load: ' + src + ' check the network tab for HTTP status.');
        onLoaded();
      };

      if (type) script.type = type;
      document.head.appendChild(script);
    });
  }

  var polyfills = [];

  if (!('fetch' in window)) {
    polyfills.push(loadScript('./polyfills/fetch.js'));
  }

  if (!('noModule' in HTMLScriptElement.prototype)) {
    polyfills.push(loadScript('./polyfills/systemjs.js'));
  }

  function loadFiles() {
    if (!('noModule' in HTMLScriptElement.prototype)) {
      System.import('./legacy/app.js');
    } else {
      loadScript('./app.js', 'module');
    }
  }

  if (polyfills.length) {
    Promise.all(polyfills).then(loadFiles);
  } else {
    loadFiles();
  }
})();