node js cli STDOUT STDERR output exec and spawn commands

I am looking for a clear answer on how the stdout and stderr work when developing a npm cli module.

I would like to print out everything exactly as it is when I run command with child_process.spawn.

I managed to output the git clone command with the --progress options. Now I want to output the npm install command but it is printing only the final string.

Would be nice to have a clear answer on how this work in general and what are the best practices.

This works:

import * as cp from 'child_process';

const child = cp.spawn('git', ['clone', 'ssh://myrepo...', '--progress']);
    
child.stdout.setEncoding('utf8');
child.stdout.on('data', (chunk) => {
    process.stdout.write(`${chunk}`);
});
    
child.stderr.setEncoding('utf8');
child.stderr.on('data', (chunk) => {
    process.stdout.write(`${chunk}`);
});

// BTW why git is outputing in STDERR and not in STDOUT?

However this doesn't work

const child = cp.spawn('npm', ['i', 'mymodule']);

Is there a way to make this work for each command?

Solution

You can leave off the event handlers and encoding settings and tell spawn() to pass stdio through to the parent process.

const child = cp.spawn('npm', ['i', 'mymodule'], {stdio: 'inherit'});

Both of your commands work for me as long as the listeners are added as in your first example. Your second example only stops working for me if I leave out the event handlers. It would be interesting to know what platform you are running on, what versions of node and npm you are using, and a complete not-working example that can be cut and paste into a file for testing. (Also, what is the name of the file? Are you using .mjs extension or something else to make import work? Is this file in a module loaded elsewhere or in the base level script?)