Smart-Polyfill is a smart modular Polyfill server written in NodeJS. It's extremely easy to extend. It allows you to send the client exactly what it needs, for example If the browser is only lacking support for String.prototype.{starts,ends}With it will send it only that and nothing more. It contains an HTTP server too, which is great in collaboration with nginx.

sudo npm install -g smart-polyfill
smart-polyfill 8080 # Replace 8080 with a port of your choice

Now navigate to http://localhost:8080/polyfill.js in a browser of your choice to see it's specific polyfills.

Adding more shims to Smart-Polyfill is as simple as writing a function, choose a file in Polyfills directory, create a new one if you want (and require it in Bin/Server.js). An example of String.prototype.startsWith shim

SmartPolyfill.register('String.prototype.startsWith', {
  Chrome: '1 - 40',
  Firefox: '1 - 16',
  IE: '*',
  Netscape: '*',
  Safari: '*'
}, function(searchString, position){
  position = position || 0;
  return this.lastIndexOf(searchString, position) === position;
});

Just drop this line in your nginx configuration's server block to proxy the polyfill.js requests through Smart-Polyfill.

  location =/polyfill.js {
    proxy_pass http://localhost:8080/polyfill.js;
  }

This project is licensed under the terms of MIT license. See the License file for more info.