Loading polyfill only when needed

Loading polyfill

const browserSupportsAllFeatures = () => window.Promise && window.fetch && window.Symbol


const loadScript = (src = '', done) =>  {
  var js = document.createElement('script')
  js.src = src
  document.head.appendChild(js)
  
  return done()
}

if (browserSupportsAllFeatures()) {
  // Browsers that support all features run `main()` immediately.
  main()
} else {
  // All other browsers loads polyfills and then run `main()`.
  loadScript('/path/to/polyfills.js', main)
}