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

const exitHook = require('async-exit-hook-improved');

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

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

// you can add async hooks by accepting a callback
exitHook(callback => {
    setTimeout(() => {
        console.log('exiting 3');
        callback();
    }, 1000);
});

// you can remove a hook
const hook = () => {
    console.log('exiting 4');
};
exitHook(hook);
exitHook.remove(hook);

// You can hook uncaught errors with uncaughtExceptionHandler(), consequently adding 
// async support to uncaught errors (normally uncaught errors result in a synchronous exit).
exitHook.uncaughtExceptionHandler(err => {
    console.error(err);
});

// You can hook unhandled rejections with unhandledRejectionHandler()
exitHook.unhandledRejectionHandler(err => {
    console.error(err);
});

// You can add multiple uncaught error handlers
// Add the second parameter (callback) to indicate async hooks
exitHook.uncaughtExceptionHandler((err, callback) => {
    sendErrorToCloudOrWhatever(err) // Returns promise
        .then(() => {
console.log('Sent err to cloud');
        })
        .catch(sendError => {
console.error('Error sending to cloud: ', err.stack);
        })
        .then(() => callback);
});

// Add exit hooks for a signal or custom message:

// Custom signal
// Arguments are `signal, exitCode` (SIGBREAK is already handled, this is an example)
exitHook.hookEvent('SIGBREAK', 21);

// process event: `message` with a filter
// filter gets all arguments passed to *handler*: `process.on(message, *handler*)`
// Exits on process event `message` with msg `customShutdownMessage` only
exitHook.hookEvent('message', 0, msg => msg !== 'customShutdownMessage');

// All async hooks will work with uncaught errors when you have specified an uncaughtExceptionHandler
throw new Error('awesome');

//=> // Sync uncaughtExcpetion hooks called and retun
//=> '[Error: awesome]'
//=> // Sync hooks called and retun
//=> 'exiting'
//=> 'exiting 2'
//=> // Async uncaughtException hooks return
//=> 'Sent error to cloud'
//=> // Sync uncaughtException hooks return
//=> 'exiting 3'

License

MIT © Tapani Moilanen
MIT © Sindre Sorhus