It's a service which accepts a request for a set of browser features and returns only the polyfills that are needed by the requesting browser.
There are lots of differing browsers and browser versions in use throughout the world, each one has a slighly different set of features to the rest. This can make developing for browsers a difficult task. The latest versions of the popular browsers can do lots of things which older browsers can not – but you may still have to support the older browsers. Polyfill.io makes it simpler to support differing browsers by attempting to recreate the missing features with polyfills: You can make use of the latest and greatest features in browsers which support them, and in those that do not.
From January 10th to January 16th, we have served 1,644,999,622 requests. 99.9922515% of which were served from Fastly's global CDN cache.