Polyfill.io · 
Polyfill.io is a service which makes web development less frustrating by selectively polyfilling just what the browser needs. Polyfill.io reads the User-Agent header of each request and returns polyfills that are suitable for the requesting browser.
Documentation
Polyfill.io documentation is on the website. Polyfill-library documentation is located here.
Contributing
Read our contributing guide to learn about our development process, how to propose bugfixes and improvements, and how to build and test your changes.
License
Polyfill.io is MIT licensed.