Doing a cleanup action just before Node.js exits

Question

I want to tell Node.js to always do something just before it exits, for whatever reason — Ctrl+C, an exception, or any other reason.

I tried th

Answer 1

"exit" is an event that gets triggered when node finish it's event loop internally, it's not triggered when you terminate the process externally.

What you're looking for is executing something on a SIGINT.

The docs at http://nodejs.org/api/process.html#process_signal_events give an example:

Example of listening for SIGINT:

// Start reading from stdin so we don't exit.
process.stdin.resume();

process.on('SIGINT', function () {
  console.log('Got SIGINT.  Press Control-D to exit.');
});

Note: this seems to interrupt the sigint and you would need to call process.exit() when you finish with your code.

Answer 2

io.js has an exit and a beforeExit event, which do what you want.

Answer 3

function fnAsyncTest(callback) {
    require('fs').writeFile('async.txt', 'bye!', callback);
}

function fnSyncTest() {
    for (var i = 0; i < 10; i++) {}
}

function killProcess() {

    if (process.exitTimeoutId) {
        return;
    }

    process.exitTimeoutId = setTimeout(() => process.exit, 5000);
    console.log('process will exit in 5 seconds');

    fnAsyncTest(function() {
        console.log('async op. done', arguments);
    });

    if (!fnSyncTest()) {
        console.log('sync op. done');
    }
}

// https://nodejs.org/api/process.html#process_signal_events
process.on('SIGTERM', killProcess);
process.on('SIGINT', killProcess);

process.on('uncaughtException', function(e) {

    console.log('[uncaughtException] app will be terminated: ', e.stack);

    killProcess();
    /**
     * @https://nodejs.org/api/process.html#process_event_uncaughtexception
     *  
     * 'uncaughtException' should be used to perform synchronous cleanup before shutting down the process. 
     * It is not safe to resume normal operation after 'uncaughtException'. 
     * If you do use it, restart your application after every unhandled exception!
     * 
     * You have been warned.
     */
});

console.log('App is running...');
console.log('Try to press CTRL+C or SIGNAL the process with PID: ', process.pid);

process.stdin.resume();
// just for testing

Answer 4

After playing around with other answer, here is my solution for this task. Implementing this way helps me centralize cleanup in one place, preventing double handling the cleanup.

1. I would like to route all other exiting codes to 'exit' code.

const others = [`SIGINT`, `SIGUSR1`, `SIGUSR2`, `uncaughtException`, `SIGTERM`]
others.forEach((eventType) => {
    process.on(eventType, exitRouter.bind(null, { exit: true }));
})

2. What the exitRouter does is calling process.exit()

function exitRouter(options, exitCode) {
   if (exitCode || exitCode === 0) console.log(`ExitCode ${exitCode}`);
   if (options.exit) process.exit();
}

3. On 'exit', handle the clean up with a new function

function exitHandler(exitCode) {
  console.log(`ExitCode ${exitCode}`);
  console.log('Exiting finally...')
}

process.on('exit', exitHandler)

For the demo purpose, this is link to my gist. In the file, i add a setTimeout to fake the process running.

If you run node node-exit-demo.js and do nothing, then after 2 seconds, you see the log:

The service is finish after a while.
ExitCode 0
Exiting finally...

Else if before the service finish, you terminate by ctrl+C, you'll see:

^CExitCode SIGINT
ExitCode 0
Exiting finally...

What happened is the Node process exited initially with code SIGINT, then it routes to process.exit() and finally exited with exit code 0.

Answer 5

Just wanted to mention death package here: https://github.com/jprichardson/node-death

Example:

var ON_DEATH = require('death')({uncaughtException: true}); //this is intentionally ugly

ON_DEATH(function(signal, err) {
  //clean up code here
})

Answer 6

This catches every exit event I can find that can be handled. Seems quite reliable and clean so far.

[`exit`, `SIGINT`, `SIGUSR1`, `SIGUSR2`, `uncaughtException`, `SIGTERM`].forEach((eventType) => {
  process.on(eventType, cleanUpServer.bind(null, eventType));
})