Miniflare is not responding once

[Kikobeats]

Current behavior

const { Miniflare } = require('miniflare')

;(async () => {
  const mf = new Miniflare({
    script: `
    addEventListener('fetch', async event => {
      event.respondWith(new Response('one'))
      event.respondWith(new Response('two'))
    })
    `
  })
  const res = await mf.dispatchFetch('http://localhost:8787/')
  console.log(await res.text()) // 'two', wrong!
})()

Expected behavior

[mrbbot]

Hey! 👋 When I try this with wrangler dev or on the playground, I actually get an exception thrown by the second respondWith. This behaviour has been implemented in Miniflare 2:

miniflare/packages/core/src/standards/event.ts

Lines 29 to 34 in 3265719

	if (this[kResponse]) {
	throw new DOMException(
	"FetchEvent.respondWith() has already been called; it can only be called once.",
	"InvalidStateError"
	);
	}

I agree that Miniflare 1's behaviour here is incorrect though. Could you try your playground example again?

[Kikobeats]

oh, first notice about v2. Is it available at npm?

[mrbbot]

Not yet, will hopefully be able to get a beta out in the next few weeks. 🤞

[mrbbot]

Hey! 👋 The first pre-release of Miniflare 2 has just been released, including this change. You can find the full changelog here and install it with npm i miniflare@next -D. Please let me know if you have any other issues, and feel free to ask questions in the #miniflare channel of the Cloudflare Workers Discord server.