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 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...

Answer 1

UPDATE:

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})); 

Answer 2

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