`onAfterResponse` does not work on Cloudflare Workers Runtime

[nzws]

What version of Elysia is running?

1.3.21

What platform is your computer?

Darwin 24.6.0 arm64 arm

What environment are you using

Cloudflare Workers (2025-09-05)

Are you using dynamic mode?

Yes

What steps can reproduce the bug?

Run this code with the npx wrangler dev ./index.ts --compatibility-date=2025-09-05 --compatibility-flags=nodejs_compat --port=3000 command:

import { Elysia } from "elysia";

export const app = new Elysia({ aot: false })
  .onRequest((ctx) => {
    console.log("onRequest", ctx.request.url);
  })
  .onBeforeHandle((ctx) => {
    console.log("onBeforeHandle", ctx.request.url);
  })
  .onAfterHandle((ctx) => {
    console.log("onAfterHandle", ctx.request.url);
  })
  .onAfterResponse((ctx) => {
    console.log("onAfterResponse", ctx.request.url);
  })
  .get("/", (ctx) => {
    console.log("Handling", ctx.request.url);
    return "Hello, world!";
  });

export default app;

What is the expected behavior?

The function registered in onAfterResponse should be executed.

onRequest http://localhost:3000/
onBeforeHandle http://localhost:3000/
Handling http://localhost:3000/
onAfterHandle http://localhost:3000/
onAfterResponse http://localhost:3000/
[wrangler:info] GET / 200 OK (6ms)

What do you see instead?

The function registered in onAfterResponse is not executed.

onRequest http://localhost:3000/
onBeforeHandle http://localhost:3000/
Handling http://localhost:3000/
onAfterHandle http://localhost:3000/
[wrangler:info] GET / 200 OK (3ms)

Additional information

This bug does not occur in v1.3.8, but it does occur starting from v1.3.9. Using git bisect, I found that this commit introduced the bug: d81da3d

This commit seems to delay the execution of onAfterResponse using setImmediate. However, based on my investigation of the Workers Runtime, it appears that functions scheduled with setImmediate are not executed once the fetch function has finished.

To work around this, I think it is necessary to wait until the setImmediate function completes by using ctx.waitUntil. However, I’m not sure how this can be achieved with elysiajs.

export default {
  async fetch(request, env, ctx) {
    const { promise, resolve } = Promise.withResolvers();

    ctx.waitUntil(promise);
    
    setImmediate(() => {
      console.log('It works');
      resolve();
    });

    setImmediate(() => {
      console.log('Not working');
    });
    
    return new Response('Hello World!');
  },
};

Have you try removing the node_modules and bun.lockb and try again yet?

Yes

[nzws]

I would prefer this bug to be fixed at the framework side. However, as a workaround until the bug is fixed, I came up with the following approach:

import { Elysia } from "elysia";
import { waitUntil } from "cloudflare:workers";

export const app = new Elysia({ aot: false })
  .onAfterResponse(() => {
    console.log("onAfterResponse 1");
  })
  .derive(() => {
    const { promise, resolve } = Promise.withResolvers();
    waitUntil(promise);

    return {
      _onAfterResponseFinished: resolve,
    }
  })
  .get("/", (ctx) => {
    console.log("Handling", ctx.request.url);
    return "Hello, world!";
  })
  .onAfterResponse(async () => {
    console.log("onAfterResponse 2 started");
    await new Promise((r) => setTimeout(r, 1000));
    console.log("onAfterResponse 2 finished");
  })
  .onAfterResponse(({ _onAfterResponseFinished }) => {
    // in final onAfterResponse
    console.log("onAfterResponse 3");
    _onAfterResponseFinished();
  });

export default app;

Handling http://localhost:3000/
onAfterResponse 1
onAfterResponse 2 started
[wrangler:info] GET / 200 OK (10ms)
onAfterResponse 2 finished
onAfterResponse 3

The important part is that, the Promise registered with waitUntil should be completed in the final onAfterResponse call.

[nzws]

I tried the Experimental Cloudflare Workers adapter that was released today, but onAfterResponse still doesn't seem to be running.

import { Elysia } from "elysia";
import { CloudflareAdapter } from "elysia/adapter/cloudflare-worker";

export const app = new Elysia({ adapter: CloudflareAdapter })
  .onRequest((ctx) => {
    console.log("onRequest", ctx.request.url);
  })
  .onBeforeHandle((ctx) => {
    console.log("onBeforeHandle", ctx.request.url);
  })
  .onAfterHandle((ctx) => {
    console.log("onAfterHandle", ctx.request.url);
  })
  .onAfterResponse((ctx) => {
    console.log("onAfterResponse", ctx.request.url);
  })
  .get("/", (ctx) => {
    console.log("Handling", ctx.request.url);
    return "Hello, world!";
  })
  .compile();

export default app;

⎔ Reloading local server...
onRequest http://localhost:3000/
onBeforeHandle http://localhost:3000/
Handling http://localhost:3000/
onAfterHandle http://localhost:3000/
[wrangler:info] GET / 200 OK (9ms)

[Vicentesan]

same with .onStart