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.

npm install exit-hook

import exitHook from 'exit-hook';

exitHook(signal => {
	console.log(`Exiting with signal: ${signal}`);
});

// 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();

Register a function to run during process.exit.

Returns a function that removes the hook when called.

Type: (signal: number) => void

The callback function to execute when the process exits.

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.

Type: (signal: number) => (void | Promise<void>)

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

Type: object

Type: number

The amount of time in milliseconds that the onExit function is expected to take. When multiple async handlers are registered, the longest wait time will be used.

import {asyncExitHook} from 'exit-hook';

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

throw new Error('🦄');

//=> 'Exiting'

Removing an asynchronous exit hook:

import {asyncExitHook} from 'exit-hook';

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

unsubscribe();

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();

Type: number
Default: 0

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

By default, nodemon uses SIGUSR2 to restart your app. Since SIGUSR2 is a user-defined signal, exit-hook does not handle it to avoid conflicts with your app logic.

Solution: Configure nodemon to use standard termination signals:

nodemon --signal SIGTERM your-app.js

Or in your nodemon.json:

{
	"signal": "SIGTERM"
}

Alternatively, you can handle SIGUSR2 in your app if you specifically need nodemon's default behavior:

// Handle nodemon restart signal
process.on('SIGUSR2', () => {
	gracefulExit();
});

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 wait time, but also be written to assume they may not complete their tasks before termination.