fetch-headers

A WHATWG-compliant Headers implementation for Node.js, version 3.0.1. It provides the standard Headers class as defined in the Fetch spec, with full support for immutable headers via the 'bag' symbol. Unlike other polyfills, this library is tested against the Web Platform Tests (WPT) and correctly handles Set-Cookie headers (iterates individually but joins all other duplicate headers with commas). It is actively maintained, ESM-only, and ships TypeScript declarations. Release cadence is irregular; latest stable is 3.0.1 as of late 2023.