Exercise 3.3 - do we need to use nextTick() ?

[stoptime]

Hi all - really enjoying this book!

I was wondering if in exercise 3.3 if we need to use the process.nextTick() function to emit a 'tick' immediately after the function is invoked? I notice that if I do not, and simply do something like emitter.emit('tick', '3.3 update') that it never fires at all, even if I remove the loop, and I'm trying to wrap my head around that... 🤔

import { EventEmitter } from 'events'
import { nextTick } from 'process'

function everyFifty(totalMil, cb) {
  let startMil = 0
  let ticks = 0
  const emitter = new EventEmitter()
  nextTick(() => emitter.emit('tick', '3.3 update')) // this will not fire w/o nextTick()

  while (startMil <= totalMil) {
    startMil += 50
    if (startMil > totalMil) {
      setTimeout(() => {
        cb(ticks)
      }, totalMil)
      break
    }
    setTimeout(() => {
      emitter.emit('tick', (ticks += 1))
    }, startMil)
  }

  return emitter
}

function finished(total) {
  console.log('completed total ticks:', total)
}

everyFifty(100, finished).on('tick', (ticks) => {
  console.log('tick', ticks)
})

// -- output --
// tick 3.3 update
// tick 1
// tick 2
// completed total ticks: 2

[mariocasciaro]

Hi Matt, thanks for reading the book. Yes you'll need a nextTick. That's essentially the main takeaway from exercise 3.3 😉. Without it, the event is emitted before the event emitter is even returned to the caller. The event fires but it's not intercepted by any listener, because there are none at the point.

…

On Fri, Feb 26, 2021, 23:48 Matt Mayes ***@***.***> wrote: Hi all - really enjoying this book! I was wondering if in exercise 3.3 if we need to use the process.nextTick() function to emit a 'tick' immediately after the function is invoked? I notice that if I do not, and simply do something like emitter.emit('tick', '3.3 update') that it never fires at all, even if I remove the loop, and I'm trying to wrap my head around that... 🤔 import { EventEmitter } from 'events' import { nextTick } from 'process' function everyFifty(totalMil, cb) { let startMil = 0 let ticks = 0 const emitter = new EventEmitter() nextTick(() => emitter.emit('tick', '3.3 update')) // this will not fire w/o nextTick() while (startMil <= totalMil) { startMil += 50 if (startMil > totalMil) { setTimeout(() => { cb(ticks) }, totalMil) break } setTimeout(() => { emitter.emit('tick', (ticks += 1)) }, startMil) } return emitter } function finished(total) { console.log('completed total ticks:', total) } everyFifty(100, finished).on('tick', (ticks) => { console.log('tick', ticks) }) // -- output -- // tick 3.3 update // tick 1 // tick 2 // completed total ticks: 2 — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#31>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAAZWZ4BXXOPBZNHGXWOAWTTBAXNJANCNFSM4YJJMPJQ> .

[stoptime]

Ah-ha! 💡 I think there was just an audible 'click' emitted from my head - thank you!