A tweak on https://www.html5rocks.com/en/tutorials/speed/script-loading/ with conditional loading for polyfills

loadScripts.js

window.loadScripts = function(scripts){
  var src;
  var script;
  var pendingScripts = [];
  var firstScript = document.scripts[0];

  // Watch scripts load in IE
  function stateChange() {
    // Execute as many scripts in order as we can
    var pendingScript;
    while (pendingScripts[0] && pendingScripts[0].readyState == 'loaded') {
      pendingScript = pendingScripts.shift();
      // avoid future loading events from this script (eg, if src changes)
      pendingScript.onreadystatechange = null;
      // can't just appendChild, old IE bug if element isn't closed
      firstScript.parentNode.insertBefore(pendingScript, firstScript);
    }
  }

  // loop through our script urls
  while (src = scripts.shift()) {
    if (src.test && src.test()) continue;

    if ('async' in firstScript) { // modern browsers
      script = document.createElement('script');
      script.async = false;
      script.src = src.src;
      document.head.appendChild(script);
    }
    else if (firstScript.readyState) { // IE<10
      // create a script and add it to our todo pile
      script = document.createElement('script');
      pendingScripts.push(script);
      // listen for state changes
      script.onreadystatechange = stateChange;
      // must set src AFTER adding onreadystatechange listener
      // else we’ll miss the loaded event for cached scripts
      script.src = src.src;
    }
    else { // fall back to defer
      document.write('<script src="' + src.src + '" defer></'+'script>');
    }
  }
}