Unhandled promise rejection in boot-loader prefetching

[neodon]

This project is exciting! Keep the momentum.

I ran into a failing unit test due to an unhandled promise rejection. I think it might have slipped by if you've only run the unit tests with an earlier version of node that just provides a warning in this situation.

Steps to reproduce:

1. Use NodeJS v16+
2. Run unit tests via yarn test.unit
3. Result:

[UnhandledPromiseRejection: This error originated either by throwing inside of an async function without a catch
block, or by rejecting a promise which was not handled with .catch(). The promise rejected with the reason
"TypeError: Cannot read property 'headers' of null".] {
  code: 'ERR_UNHANDLED_REJECTION'
}
 FAIL  src/bootloader-shared.unit.ts
  ● Test suite failed to run

    Jest worker encountered 4 child process exceptions, exceeding retry limit

      at ChildProcessWorker.initialize (node_modules/jest-worker/build/workers/ChildProcessWorker.js:193:21)

The error appears to originate in the setUpWebWorker() function in src/bootloader-shared.ts. Specifically, this statement:

((await fetch(url)).headers.get('Link') || '').replace(
  /<([^>]*)>/g,
  prefetch as any as (_: string, url: string) => string
);

We're expecting fetch(url) to return a response with a headers key. The mock for fetch in the unit test, however, returns null:

const mockFetch = jest.fn(() => null);

I tried changing the mock to provide the minimal response object to avoid an error, and it appears to resolve the issue:

const mockFetch = jest.fn(() => ({ headers: { get: () => {}}}));

  prefetch
    setUpWebWorker
      ✓ should listen on events and fire fetch

Is this the correct way to resolve the issue? If so, I could submit a pull request.

I appreciate any insight you can provide as well. Thanks!

[neodon]

Looks like this is already fixed in mhevery:functional.