foreground-child

What is foreground-child?

The foreground-child npm package is used to run a child process in the foreground, ensuring that signals such as SIGINT, SIGTERM, and exit codes are properly forwarded from the child process to the parent. This is particularly useful when you want to ensure that a child process is treated as if it were the main process, especially in the context of command-line tools and scripts.

What are foreground-child's main functionalities?

Running a child process in the foreground

This feature allows you to run a child process as if it were the main process. The code sample demonstrates how to use foreground-child to run a Node.js script in the foreground.

const foregroundChild = require('foreground-child');

const cmd = 'node';
const args = ['my-script.js'];
foregroundChild(cmd, args);

Other packages similar to foreground-child

cross-spawn

cross-spawn is a cross-platform solution for spawning child processes with support for handling command line arguments properly. It is similar to foreground-child in that it deals with child processes, but it does not specifically focus on running them in the foreground.

execa

execa is a wrapper for child_process methods that provides a more user-friendly API. It supports synchronous and asynchronous execution of child processes and also allows for running processes in the foreground, similar to foreground-child, but with additional features such as promise support and result parsing.

child-process-promise

child-process-promise provides promise-based wrappers for the child_process module. While it simplifies working with asynchronous child processes, it does not have a specific focus on running child processes in the foreground like foreground-child does.

README

foreground-child

Run a child as if it's the foreground process. Give it stdio. Exit when it exits.

Mostly this module is here to support some use cases around wrapping child processes for test coverage and such.

USAGE

var foreground = require('foreground-child')

// cats out this file
var child = foreground('cat', [__filename])

// At this point, it's best to just do nothing else.
// return or whatever.
// If the child gets a signal, or just exits, then this
// parent process will exit in the same way.

A callback can optionally be provided, if you want to perform an action before your foreground-child exits:

var child = foreground('cat', [__filename], function (done) {
  // perform an action.
  return done()
})

The callback can return a Promise instead of calling done:

var child = foreground('cat', [__filename], async function () {
  // perform an action.
})

The callback must not throw or reject.

Caveats

The "normal" standard IO file descriptors (0, 1, and 2 for stdin, stdout, and stderr respectively) are shared with the child process. Additionally, if there is an IPC channel set up in the parent, then messages are proxied to the child on file descriptor 3.

However, in Node, it's possible to also map arbitrary file descriptors into a child process. In these cases, foreground-child will not map the file descriptors into the child. If file descriptors 0, 1, or 2 are used for the IPC channel, then strange behavior may happen (like printing IPC messages to stderr, for example).

Note that a SIGKILL will always kill the parent process, and never the child process, because SIGKILL cannot be caught or proxied. The only way to do this would be if Node provided a way to truly exec a process as the new foreground program in the same process space, without forking a separate child process.