events.md

Events

nodemon will emit events based on the child process.

Commands

• restart
• config:update
• quit

States

• start - child process has started
• crash - child process has crashed (nodemon will not emit exit)
• exit - child process has cleanly exited (ie. no crash)
• restart([ array of files triggering the restart ]) - child process has restarted
• config:update - nodemon's config has changed

Messages

• log({ type, message (plain text log), colour (colour coded log) }) - logging from nodemon (not the child process)
• stdout - the stdout stream from the child process
• stderr - the stderr stream from the child process
• readable - stdout and stderr streams are ready (example)

Note that if you want to supress the normal stdout & stderr of the child, in favour of processing the stream manually using the stdout/stderr nodemon events, pass nodemon the option of stdout: false.

Using nodemon events

If nodemon is required, events can be bound and emitted on the nodemon object:

var nodemon = require('nodemon');

nodemon({ script: 'app.js' }).on('start', function () {
  console.log('nodemon started');
}).on('crash', function () {
  console.log('script crashed for some reason');
});

// force a restart
nodemon.emit('restart');

// force a quit
nodemon.emit('quit');

Using nodemon as child process

If nodemon is a spawned process, then the child (nodemon) will emit message events whereby the event argument contains the event type, and instead of emitting events, you send the command:

// using `spawn` as example, can use other functions like `fork`, etc
// https://nodejs.org/api/child_process.html
const { spawn } = require('child_process');

function spawnNodemon() {
  const cp = spawn('nodemon', ['path/to/file.js', '--watch', 'path/to/watch'], {
    // the important part is the 4th option 'ipc'
    // this way `process.send` will be available in the child process (nodemon)
    // so it can communicate back with parent process (through `.on()`, `.send()`)
    // https://nodejs.org/api/child_process.html#child_process_options_stdio
    stdio: ['pipe', 'pipe', 'pipe', 'ipc'],
  });

  return cp;
}

var app = spawnNodemon();

app.on('message', function (event) {
  if (event.type === 'start') {
    console.log('nodemon started');
  } else if (event.type === 'crash') {
    console.log('script crashed for some reason');
  }
});

// force a restart
app.send('restart');

// force a quit
app.send('quit');

Note that even though the child will still emit a message event whose type is exit, it makes more sense to listen to the actual exit event on the child:

app.on('exit', function () {
  console.log('nodemon quit');
});