Explaining Microtasks and Macrotasks in Node

mi(a)cro-task.js

console.log('script start')

const interval = setInterval(() => {
  console.log('setInterval')
}, 0)

setTimeout(() => {
  console.log('setTimeout 1')
  Promise.resolve().then(() => {
    console.log('promise 3')
  }).then(() => {
    console.log('promise 4')
  }).then(() => {
    setTimeout(() => {
      console.log('setTimeout 2')
      Promise.resolve().then(() => {
        console.log('promise 5')
      }).then(() => {
        console.log('promise 6')
      }).then(() => {
        clearInterval(interval)
      })
    }, 0)
  })
}, 0)

Promise.resolve().then(() => {
  console.log('promise 1')
}).then(() => {
  console.log('promise 2')
})

script start
promise1
promise2
setInterval
setTimeout1
promise3
promise4
setInterval
setTimeout2
setInterval
promise5
promise6

Why use process.nextTick()?

There are two main reasons:

• Allow users to handle errors, cleanup any then unneeded resources, or perhaps try the request again before the event loop continues.

• At times it's necessary to allow a callback to run after the call stack has unwound but before the event loop continues.