A polyfill server is included with Koala. This might seem like an odd feature to add to a framework, but the goal is much broader. Part of the reason we have such a crazy mess with front-end package managers is because we need to create a lot of tiny modules that resolve browser inconsistencies, specifically to support old JS APIs. The easiest thing to do is just polyfill old browsers and ditch all these tiny modules.
However, you don't want to have the latest browsers download 50kb of polyfills
when all it needs is 5kb.
This is the purpose of polyfills - serve polyfill bundles based on the
client's user-agent, giving them only what they need.
Add <script src="/polyfill.js"></script> to your page,
and the appropriate polyfills will be used on the page.