Node child process event listen

This works for me:

var child_process = require('child_process');var cmd = 'ls';var value = ['-z', '/usr'];var opt = { };var child = child_process.spawn(cmd, value, opt);child.stdout.on('data', function (data) {    console.log("IM HERE");    console.log('data' + data);});child.stderr.on('data', function (data) {    console.log("IM HERE - Error");    console.log('test: ' + data);});child.on('close', function (code) {    console.log("IM HERE");    console.log("close");});

Console output:

/*IM HERE - Errortest: ls: invalid option -- 'z'Try 'ls --help' for more information.IM HEREclose*/

The issue in your side, maybe the command you're spawning doesn't use stderr?

Update

If I add process.exit()

var child_process = require('child_process');var cmd = 'ls';var value = ['-z', '/usr'];var opt = { };var child = child_process.spawn(cmd, value, opt);child.stdout.on('data', function (data) {    console.log("IM HERE");    console.log('data' + data);});child.stderr.on('data', function (data) {    console.log("IM HERE - Error");    console.log('test: ' + data);    process.exit(1); // <<<< this works as expected and exit the process asap});child.on('close', function (code) {    console.log("IM HERE");    console.log("close");});

The ouput is slightly different (no close event from the child)

/*IM HERE - Errortest: ls: invalid option -- 'z'Try 'ls --help' for more information.*/

You can "play" with the code here: https://tonicdev.com/shanshan/cp-spawn-piping

You can subscribe to the data event(stdout or stderr) and listen it

child.stdout.on('data', function (buf) {    console.log(buf.toString());});

For example

const spawn = require('child_process').spawn;const child = spawn('ping', ['google.com']);child.stdout.on('data', function (buf) {    console.log('buf receive');    console.log(buf.toString());});