async-exit-hook-improved

Run some code when the process exits

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

• process SIGINT, SIGTERM and SIGHUP, SIGBREAK signals
• process beforeExit and exit events
• PM2 clustering process shutdown message (PM2 graceful reload)

Useful for cleaning up. You can also include async handlers, and add custom events to hook and exit on.

Forked and pretty much rewritten from exit-hook.

Install

$ npm install --save async-exit-hook-improved

Usage

Considerations and warning

On process.exit() and asynchronous code

If you use asynchronous exit hooks, DO NOT use process.exit() to exit. The exit event DOES NOT support asynchronous code.

['beforeExit' is not emitted for conditions causing explicit termination, such as process.exit()] (https://nodejs.org/api/process.html#process_event_beforeexit)

Windows and process.kill(signal)

On windows process.kill(signal) immediately kills the process, and does not fire signal events, and as such, cannot be used to gracefully exit. See Clustering and child processes for a workaround when killing child processes. I'm planning to support gracefully exiting with async support on windows soon.

Clustering and child processes

If you use custom clustering / child processes, you can gracefully shutdown your child process by sending a shutdown message (childProc.send('shutdown')).

Example

1const exitHook = require('async-exit-hook-improved');
2
3exitHook(() => {
4    console.log('exiting');
5});
6
7// you can add multiple hooks, even across files
8exitHook(() => {
9    console.log('exiting 2');
10});
11
12// you can add async hooks by accepting a callback
13exitHook(callback => {
14    setTimeout(() => {
15        console.log('exiting 3');
16        callback();
17    }, 1000);
18});
19
20// you can remove a hook
21const hook = () => {
22    console.log('exiting 4');
23};
24exitHook(hook);
25exitHook.remove(hook);
26
27// You can hook uncaught errors with uncaughtExceptionHandler(), consequently adding 
28// async support to uncaught errors (normally uncaught errors result in a synchronous exit).
29exitHook.uncaughtExceptionHandler(err => {
30    console.error(err);
31});
32
33// You can hook unhandled rejections with unhandledRejectionHandler()
34exitHook.unhandledRejectionHandler(err => {
35    console.error(err);
36});
37
38// You can add multiple uncaught error handlers
39// Add the second parameter (callback) to indicate async hooks
40exitHook.uncaughtExceptionHandler((err, callback) => {
41    sendErrorToCloudOrWhatever(err) // Returns promise
42        .then(() => {
43console.log('Sent err to cloud');
44        })
45        .catch(sendError => {
46console.error('Error sending to cloud: ', err.stack);
47        })
48        .then(() => callback);
49});
50
51// Add exit hooks for a signal or custom message:
52
53// Custom signal
54// Arguments are `signal, exitCode` (SIGBREAK is already handled, this is an example)
55exitHook.hookEvent('SIGBREAK', 21);
56
57// process event: `message` with a filter
58// filter gets all arguments passed to *handler*: `process.on(message, *handler*)`
59// Exits on process event `message` with msg `customShutdownMessage` only
60exitHook.hookEvent('message', 0, msg => msg !== 'customShutdownMessage');
61
62// All async hooks will work with uncaught errors when you have specified an uncaughtExceptionHandler
63throw new Error('awesome');
64
65//=> // Sync uncaughtExcpetion hooks called and retun
66//=> '[Error: awesome]'
67//=> // Sync hooks called and retun
68//=> 'exiting'
69//=> 'exiting 2'
70//=> // Async uncaughtException hooks return
71//=> 'Sent error to cloud'
72//=> // Sync uncaughtException hooks return
73//=> 'exiting 3'

License

MIT © Tapani Moilanen
MIT © Sindre Sorhus