polyfillpolyfill/polyfill-service

Polyfill Service is a server that automatically selects and delivers JavaScript polyfills based on the requesting browser's capabilities. It reads the User-Agent header of each request to determine which polyfills are needed, ensuring that only the code required for that specific browser is served.

The service assembles polyfill bundles on the server at request time, generating custom JavaScript payloads per client. It uses runtime feature detection to decide which polyfills to include, avoiding unnecessary code for modern browsers, and sends these bundles as streaming responses for progressive loading. A versioned polyfill repository allows precise matching of polyfill versions to browser requirements.

The project maintains a collection of polyfills that can be conditionally loaded based on browser support, reducing payload size for modern browsers while ensuring compatibility for older ones.