exit-hook

Run some code when the process exits

The process.on('exit') event doesn't catch all the ways a process can exit.

This package is useful for cleaning up before exiting.

Install

npm install exit-hook

Usage

import exitHook from 'exit-hook';

exitHook(() => {
	console.log('Exiting');
});

// You can add multiple hooks, even across files
exitHook(() => {
	console.log('Exiting 2');
});

throw new Error('🦄');

//=> 'Exiting'
//=> 'Exiting 2'

Removing an exit hook:

import exitHook from 'exit-hook';

const unsubscribe = exitHook(() => {});

unsubscribe();

API

exitHook(onExit)

Register a function to run during process.exit.

Returns a function that removes the hook when called.

onExit

Type: function(): void

The callback function to execute when the process exits.

asyncExitHook(onExit, minimumWait)

Register a function to run during gracefulExit.

Returns a function that removes the hook when called.

Please see Async Notes for considerations when using the asynchronous API.

import {asyncExitHook} from 'exit-hook';

asyncExitHook(async () => {
	console.log('Exiting');
}, 300);

throw new Error('🦄');

//=> 'Exiting'

Removing an asynchronous exit hook:

import {asyncExitHook} from 'exit-hook';

const unsubscribe = asyncExitHook(async () => {
	console.log('Exiting');
}, {
	minimumWait: 300
});

unsubscribe();

onExit

Type: function(): void | Promise<void>

The callback function to execute when the process exits via gracefulExit, and will be wrapped in Promise.resolve.

options

minimumWait

Type: number

The amount of time in milliseconds that the onExit function is expected to take.

gracefulExit(signal?: number): void

Exit the process and make a best-effort to complete all asynchronous hooks.

If you are using asyncExitHook, consider using gracefulExit() instead of process.exit() to ensure all asynchronous tasks are given an opportunity to run.

import {gracefulExit} from 'exit-hook';

gracefulExit();

signal

Type: number
Default: 0

The exit code to use. Same as the argument to process.exit().

Asynchronous Exit Notes

tl;dr If you have 100% control over how your process terminates, then you can swap exitHook and process.exit for asyncExitHook and gracefulExit respectively. Otherwise, keep reading to understand important tradeoffs if you're using asyncExitHook.

Node.js does not offer an asynchronous shutdown API by default #1 #2, so asyncExitHook and gracefulExit will make a "best effort" attempt to shut down the process and run your asynchronous tasks.

If you have asynchronous hooks registered and your Node.js process is terminated in a synchronous manner, a SYNCHRONOUS TERMINATION NOTICE error will be logged to the console. To avoid this, ensure you're only exiting via gracefulExit or that an upstream process manager is sending a SIGINT or SIGTERM signal to Node.js.

Asynchronous hooks should make a "best effort" to perform their tasks within the minimumWait time, but also be written to assume they may not complete their tasks before termination.