fork-with-emitter

Simple EventEmitter wrapper for IPC, enhanced with async .request().

• Zero dependencies.
• TypeScript support.
• Intuitive naming (fork/host).

Basics

bot.js (fork):

const { host } = require('fork-with-emitter')

host.on('hello', name => {
  console.log(`Hello ${name}`)
})

host.onRequest('getRandomNumber', async () => {
  await sleep(1000)
  return Math.floor(Math.random() * 1000)
})

//returns promise that resolves after given ms
const sleep = ms => 
  new Promise(res => setTimeout(res, ms))

index.js (host):

const { createFork } = require('fork-with-emitter')

const fork = createFork('bot.js')
//pipe fork's console.log to host's console.log
fork.process.stdout.pipe(process.stdout)

fork.emit('hello', 'Artur')

;(async () => {
  const randomNumber = await fork.request('getRandomNumber')
  console.log(randomNumber)

  fork.kill()
})()

Output:

Hello Artur
623

Handling errors

bot.js (fork):

const { host } = require('fork-with-emitter')

host.onRequest('throwError', async () => {
  throw new Error(`Some error message`)
})

index.js (host):

const { createFork } = require('fork-with-emitter')

const fork = createFork('bot.js')

;(async () => {
  try {
    await fork.request('throwError')
  } catch(error) {
    console.log(error)
  }
})()

Output:

Error: Some error message
    at (fork's stack)

Errors and rejections are captured only from .onRequest() handlers.

Exports

{
  /*
    Returns new spawned fork.
  */
  createFork(modulePath, options = { args: [] }),

  /*
    Variable indicating if process is a fork. 
  */
  isForked,

  /*
    Points to host (use those methods from fork).
  */
  host: {
    /*
      process.on('message', listener) with events
    */
    on(event, listener),

    /*
      Listener is removed after execution.
    */
    once(event, listener),

    removeListener(event, listener),

    /*
      process.send(payload) with events
    */
    emit(event, listener),

    /*
      Returned/resolved data from async function will be passed to host's request.  
    */
    onRequest(event, listener),

    onceRequest(event, listener),

    removeRequestListener(event, listener),

    /*
      Returns Promise that resolves with data resolved from host's .onRequest() listener.
      Rejects if response is not sent after 10 seconds.
      maximumTimeout = Infinity -> for very long tasks, not recommended though, because if task stucks and fork still works it causes a memory leak.
    */
    request(event, listener, maximumTimeout = 10)
  }
}

Fork object

Object that points to spawned fork.

{
  /*
    Native ChildProcess object.
  */
  process,

  /*
    Exits process with SIGINT.
  */
  kill(),

  on(event, listener),
  once(event, listener),
  removeListener(event, listener),
  emit(event, listener),
  onRequest(event, listener),
  onceRequest(event, listener),
  removeRequestListener(event, listener),
  request(event, listener, maximumTimeout = 10)
}

License

MIT