Node: cannot debug node child process (using node native debugger)

Created on 21 Sep 2016 · 8Comments · Source: nodejs/node

I'm trying to debug node child process, using native node debugger. See this repo for example.

I tried all king of options, according to: debug1, debug1, debug3 (and a lot of other references I found online).

Non of those options worked for me..

This is my example code:

index.js:

const spawn = require('child_process').spawn;
const path = require('path');

const ls = spawn('node', [path.resolve('./child.js')], {execArgv: '--debug-brk=4545'});

ls.stdout.on('data', (data) => {
  console.log(`stdout: ${data}`);
});

ls.stderr.on('data', (data) => {
  console.log(`stderr: ${data}`);
});

ls.on('close', (code) => {
  console.log(`child process exited with code ${code}`);
});

child.js:

debugger;
const a = 123;

console.log(a);

I then run:

node --debug-brk --inspect=9222 index.js

And I open the chrome-devtools://devtools/... in chrome. Debugging the main process works great, and I see the child process output as well. Only thing that is not working is debug of child process...

What am I doing wrong here?

inspector question

Source

yanivefraim

👍2

Most helpful comment

That doesn't work for spawn(), you may be thinking of fork(). Explicitly pass --inspect=... as an argument and it should work, i.e.:

const file = path.resolve('./child.js');
const args = ['--inspect=9223', file];
const proc = cp.spawn(process.execPath, args);

bnoordhuis on 21 Sep 2016

👍6

All 8 comments

If you are spawning child processes, you need to pass --inspect=<port> to them and give each child process its own unique port number. You will need to open a separate devtools instance for each process.

bnoordhuis on 21 Sep 2016

Thanks @bnoordhuis - i tried that without success, maybe I'm doing something wrong?

In my example, I tried (inside index.js):

process.execArgv.push('--inspect=' + (9223));

const ls = child.spawn('node', [path.resolve('./child.js')]);

I then opened both child and index devtools (child first and then index). I was expecting to hit breakpoints on child while running index.js, but it didn't work

yanivefraim on 21 Sep 2016

That doesn't work for spawn(), you may be thinking of fork(). Explicitly pass --inspect=... as an argument and it should work, i.e.:

const file = path.resolve('./child.js');
const args = ['--inspect=9223', file];
const proc = cp.spawn(process.execPath, args);

bnoordhuis on 21 Sep 2016

👍6

Thanks! This is working now. I really think we should add docs for debugging child processes/cluster to the node debug section. This can be really tricky and documentation almost doesn't exists!

yanivefraim on 21 Sep 2016

👍4

You can open a documentation pull request if you want, the files to look for are in doc/api.

bnoordhuis on 22 Sep 2016

👍1

@yanivefraim : I follow the suggestion but it is not working at all. Here is my code for start spawn process:

server = cp.spawn('node', [serverPath, '--inspect=9223'], {
env: Object.assign({ NODE_ENV: 'development' }, process.env),
silent: false,
});

Could you help? Is there anything wrong here?