Automatic polyfill

polyfillmeup.html

<!--source-->
<script type="text/javascript">
(function(){
  if (!(
    "Promise" in window &&
    "fetch" in window &&
    "assign" in Object &&
    "keys" in Object
  )) {
    var polyfill = document.createElement("script");
    polyfill.src = "https://cdn.polyfill.io/v2/polyfill.min.js";
    polyfill.async = false;
    document.head.appendChild(polyfill);
  }
})();
</script>

<!--minified-->
<script type="text/javascript">(function(){if(!("fetch"in window&&"Promise"in window&&"assign"in Object&&"keys"in Object)){var a=document.createElement("script");a.src="https://cdn.polyfill.io/v2/polyfill.min.js";a.async=!1;document.head.appendChild(a)}})();</script>