Wrong instanceof behavior when extending Error

[valeriangalliat]

Hey! I'm running in the following inconsistency between Miniflare's engine (2.2.0) and other JS runtimes (including the Cloudflare runtime).

Consider the following worker:

class TestError extends Error {}

addEventListener('fetch', event => {
  event.respondWith(handleRequest(event.request))
})

async function handleRequest(request) {
  console.log(new Error() instanceof TypeError)
  console.log(new TypeError() instanceof Error)
  console.log(new TestError() instanceof Error)
  console.log(new TestError() instanceof TypeError)
  console.log(new TestError() instanceof TestError)
  console.log(new Error() instanceof TestError)
  console.log(new TypeError() instanceof TestError)

  return new Response('', {
    headers: { 'content-type': 'text/plain' },
  })
}

On Miniflare, it logs:

false
true
true
false
true
true
true

Whereas with wrangler dev (or just in Node.js or any browser), it logs:

false
true
true
false
true
false
false

The behaviour is correct for native errors but as soon as we extend Error, every error is considered to be instanceof our custom error on Miniflare.

Cheers!

[mrbbot]

Uh oh! 😟 That's not good! Will be fixed in the next version. 👍

[mrbbot]

Hey! 👋 I've just released version 2.3.0 including a fix for this. You can find the full changelog here.

[valeriangalliat]

Awesome, thanks for the fix and the heads up! ❤️