There are various ways to terminate a Node.js application.

When running a program in the console you can close it with ctrl-C, but what I want to discuss here is programmatically exiting.

Let’s start with the most drastic one, and see why you’re better off not using it.

The process core module provides a handy method that allows you to programmatically exit from a Node.js program: process.exit().

When Node.js runs this line, the process is immediately forced to terminate.

This means that any callback that’s pending, any network request still being sent, any filesystem access, or processes writing to stdout or stderr - all will be ungracefully terminated right away.

If this is fine for you, you can pass an integer that signals the exit code to the operating system:

process.exit(1)

By default the exit code is 0, which means success. Different exit codes have different meaning, which you might want to use in your own system to have the program communicate to other programs.

You can read more on exit codes at https://nodejs.org/api/process.html#process_exit_codes

You can also set the process.exitCode property:

process.exitCode = 1

and when the program later ends, Node will return that exit code.

A program will gracefully exit when all processing is done.

Many times with Node we start servers, like this HTTP server:

const express = require('express')
const app = express()

app.get('/', (req, res) => {
  res.send('Hi!')
})

app.listen(3000, () => console.log('Server ready'))

This program is never going to end. If you call process.exit(), any currently pending or running requests will be aborted. This is not nice.

In this case you need to send the command a SIGTERM signal, and handle that with the process signal handler:

Note: process does not require a “require”, it’s automatically available.

const express = require('express')

const app = express()

app.get('/', (req, res) => {
  res.send('Hi!')
})

const server = app.listen(3000, () => console.log('Server ready'))

process.on('SIGTERM', () => {
  server.close(() => {
    console.log('Process terminated')
  })
})

What are signals? Signals are a POSIX intercommunication system: a notification sent to a process in order to notify it of an event that occurred.

SIGKILL is the signal that tells a process to immediately terminate, and would ideally act like process.exit().

SIGTERM is the signal that tells a process to gracefully terminate. It is the signal that’s sent from process managers like upstart or supervisord and many others.

You can send this signal from inside the program, in another function:

process.kill(process.pid, 'SIGTERM')

Or from another Node.js running program, or any other app running in your system that knows the PID of the process you want to terminate.

Lessons in this unit:

0:	Introduction
1:	How to execute a shell command using Node.js
2:	How to spawn a child process with Node.js
3:	Node, accept arguments from the command line
4:	Accept input from the command line in Node
5:	How to log an object in Node
6:	Output to the command line using Node
7:	▶︎ How to exit from a Node.js program