Last Words

Run some (cleanup) code before the process exits.

Listens to:

• ['SIGTERM', 'SIGINT', 'SIGQUIT', 'SIGHUP', 'SIGBREAK']

  1. cb(false)
  2. Node exits when event loop is emptied

• uncaughtExceptionMonitor

  1. cb(true, err) on uncaughtException (and unhandledRejection based on --unhandled-rejections flag)
  2. Node logs the error to stderr and exits

• exit

  1. cb(true)
  2. Node exits

Usage

const onExit = require('last-words')

onExit((
  abort, // true / false
  err // instanceof Error when `uncaughtException`/`unhandledRejection`
) => {
  if (abort) {
    // only perform sync tasks
  } else {
    // can perform async tasks
  }
})

Considerations

• It does not explicitly kill the process and will be terminated by Node when the event loop is emptied. Therefore, if you forget to cleanup some holding processes, it will not be terminated.

• If the process is killed with "preventable" signals (other than e.g. SIGKILL or explicit process.exit()), the callback will be invoked twice. Once with abort = false and again with abort = true. An exception is uncaughtException/unhandledRejection - those will callback twice with abort = true

Alternatives and differences

It calls a hook on exiting when there is time for async cleanup and when there is not and let Node exit naturally. If there is something still holding the process, it doesn't timeout, thus allowing spotting developer bugs.

There are alternatives out there developed to tackle the same task. Most of them are either not maintained anymore, an overkill with functionality, exits the process explicitly or handles and prevents uncaughtException by default.

• async-exit-hook

  • calls process.exit explicitly
  • custom hooks
  • async timeout
  • uncaughtException/unhandledRejection hooks (can not opt-out)
  • hooks cleanup functionality

• node-graceful

  • calls process.exit explicitly
  • custom hooks
  • async timeout
  • uncaughtException/unhandledRejection hooks
  • hooks cleanup functionality

• node-cleanup

  • calls process.exit explicitly
  • uncaughtException hook (can not opt-out)
  • custom hooks
  • custom stderr messages

• death

  • uncaughtException hook