polyfill.io for old browsers only

polyfills.html

<!--
Only load polyfills for old browsers
@see https://devhints.io/polyfill.io
@see https://polyfill.io
-->
<script>if(!(window.Promise&&[].includes&&Object.assign&&window.Map)){document.write('<script src="https://cdn.polyfill.io/v3/polyfill.min.js"></scr'+'ipt>')}</script>

<!-- Same as above, but also loads Fetch API polyfill -->
<script>if(!(window.fetch&&window.Promise&&[].includes&&Object.assign&&window.Map)){document.write('<script src="https://cdn.polyfill.io/v3/polyfill.min.js?features=default,fetch"></scr'+'ipt>')}</script>