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 this:
process.on('exit', function (){
console.log('Goodbye!');
});
I started the process, killed it, and nothing happened. I started it again, pressed Ctrl+C, and still nothing happened...
You can register a handler for process.on('exit') and in any other case(SIGINT or unhandled exception) to call process.exit()
process.stdin.resume();//so the program will not close instantly
function exitHandler(options, exitCode) {
if (options.cleanup) console.log('clean');
if (exitCode || exitCode === 0) console.log(exitCode);
if (options.exit) process.exit();
}
//do something when app is closing
process.on('exit', exitHandler.bind(null,{cleanup:true}));
//catches ctrl+c event
process.on('SIGINT', exitHandler.bind(null, {exit:true}));
// catches "kill pid" (for example: nodemon restart)
process.on('SIGUSR1', exitHandler.bind(null, {exit:true}));
process.on('SIGUSR2', exitHandler.bind(null, {exit:true}));
//catches uncaught exceptions
process.on('uncaughtException', exitHandler.bind(null, {exit:true}));
The script below allows having a single handler for all exit conditions. It uses an app specific callback function to perform custom cleanup code.
cleanup.js
// Object to capture process exits and call app specific cleanup function
function noOp() {};
exports.Cleanup = function Cleanup(callback) {
// attach user callback to the process event emitter
// if no callback, it will still exit gracefully on Ctrl-C
callback = callback || noOp;
process.on('cleanup',callback);
// do app specific cleaning before exiting
process.on('exit', function () {
process.emit('cleanup');
});
// catch ctrl+c event and exit normally
process.on('SIGINT', function () {
console.log('Ctrl-C...');
process.exit(2);
});
//catch uncaught exceptions, trace, then exit normally
process.on('uncaughtException', function(e) {
console.log('Uncaught Exception...');
console.log(e.stack);
process.exit(99);
});
};
This code intercepts uncaught exceptions, Ctrl+C and normal exit events. It then calls a single optional user cleanup callback function before exiting, handling all exit conditions with a single object.
The module simply extends the process object instead of defining another event emitter. Without an app specific callback the cleanup defaults to a no op function. This was sufficient for my use where child processes were left running when exiting by Ctrl+C.
You can easily add other exit events such as SIGHUP as desired. Note: per NodeJS manual, SIGKILL cannot have a listener. The test code below demonstrates various ways of using cleanup.js
// test cleanup.js on version 0.10.21
// loads module and registers app specific cleanup callback...
var cleanup = require('./cleanup').Cleanup(myCleanup);
//var cleanup = require('./cleanup').Cleanup(); // will call noOp
// defines app specific callback...
function myCleanup() {
console.log('App specific cleanup code...');
};
// All of the following code is only needed for test demo
// Prevents the program from closing instantly
process.stdin.resume();
// Emits an uncaught exception when called because module does not exist
function error() {
console.log('error');
var x = require('');
};
// Try each of the following one at a time:
// Uncomment the next line to test exiting on an uncaught exception
//setTimeout(error,2000);
// Uncomment the next line to test exiting normally
//setTimeout(function(){process.exit(3)}, 2000);
// Type Ctrl-C to test forced exit
"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.
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
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
})
async-exit-hook seems to be the most up-to-date solution for handling this problem. It's a forked/re-written version of exit-hook that supports async code before exiting.
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.
const others = [`SIGINT`, `SIGUSR1`, `SIGUSR2`, `uncaughtException`, `SIGTERM`]
others.forEach((eventType) => {
process.on(eventType, exitRouter.bind(null, { exit: true }));
})
function exitRouter(options, exitCode) {
if (exitCode || exitCode === 0) console.log(`ExitCode ${exitCode}`);
if (options.exit) process.exit();
}
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.
