A undici fetch Polyfill shamelessly ripped from Next.js

node-polyfill-fetch.js

import Undici from "undici";

// Polyfill fetch() in the Node.js environment
// Simplified from https://github.com/vercel/next.js/blob/canary/packages/next/src/server/node-polyfill-fetch.ts

if (!global.fetch) {
  function getFetchImpl() {
    return Undici;
  }

  global.fetch = (...args) => {
    const fetchImpl = getFetchImpl();

    fetchImpl.setGlobalDispatcher(new fetchImpl.Agent({ pipelining: 0 }))

    return fetchImpl.fetch(...args);
  }

  Object.defineProperties(global, {
    Headers: {
      get() {
        return getFetchImpl().Headers
      },
    },
    Request: {
      get() {
        return getFetchImpl().Request
      },
    },
    Response: {
      get() {
        return getFetchImpl().Response
      },
    },
  })
}