the child process created by child_process.fork can't receive message correctly when using ES module

[xiefenga]

• Version: v16.4.0、v14.17.1
• Platform: Windows 10 x64
• Subsystem: child_process

What steps will reproduce the bug?

when using ES module and child_process to fork child process, even 'spawn' event has happend，child process failed receive message from parent process.

Complete Testcase

package.json:

{
  "type": "module"
}

master.js

import { join } from 'path'
import { fork } from 'child_process'
import { fileURLToPath } from 'url'

const __dirname = join(
  fileURLToPath(import.meta.url),
  '../'
)

const worker = fork(
  join(__dirname, './worker.js')
);

worker.on('spawn', () => {
  console.log('start success');
  worker.send('hello', () => console.log('send success'));
});

worker.js

console.log('child process has started, processID:', process.pid);

process.on('message', (msg) => {
  console.log('child process get msg:', msg);
});

console ouput:

start success
send success
child process has started, processID: 6224

if i delay 1s send message to child process, it works:

worker.on('spawn', () => {
  console.log('start success');
  setTimeout(() => {
    worker.send('hello', () => console.log('send success'));
  }, 1000);
});

console output:

start success
child process has started, processID: 18156
send success
child process get msg: hello

What is the expected behavior?

the expected behavior just like this:

start success
send success
child process has started, processID: 16428
child process get msg: hello

when i rename worker.js to worker.cjs, got expected result.

Possible cause

I suspect this may have something to do with ESM asynchronous execution.

[Linkgoron]

I think that this is a duplicate of #37782

tl;dr, yes this is an issue with how loading is now async, and the message is emitted too early before having an option to register

[huseyinacacak-janea]

Hi @xiefenga, I wanted to look into this issue but wasn't able to reproduce it (I tried Node.js v18.20.4, v20.18.0, v22.10.0, and v23.1.0).
Do you think this issue can be closed now?

[xiefenga]

maybe it has been fixed in new version

[xiefenga]

but i can't judge whethor can close this issue or not

[xiefenga]

i tried in v20.15.0, it worked as expected, i think this issue can be closed