process.nextTick vs Promise Microtasks

·Medium·Node Event Loop

Node's two microtask queues, and which one drains first

Practice mode

Step

The main module runs

Requiring and executing the entry file is synchronous work, before the event loop starts at all.

Algorithm workspace

Execution

Step 1 / 12init

100%

node

timers

→pending

→poll (I/O)

→check

→close

↻

running: main script

Call stack

main module

Queues

process.nextTickmicrotask

drains first, and fully — even callbacks added while draining

empty

Microtasks (promises)microtask

drains after nextTick, between every phase

empty

Console output

1start

Node has two microtask queues · nextTick drains completely first, then promises — then nextTick is checked again

Explanation

Node runs the whole main module first, then drains both microtask queues, and only then enters the event loop's first turn.

step 1 / 12

Space play← → stepHome reset

Time—·SpaceO(n) queued callbacks

Execution

1console.log('start');//output: 1
2 
3process.nextTick(() => {
4  console.log('nextTick 1');
5  process.nextTick(() => console.log('nextTick 2'));
6});
7 
8Promise.resolve().then(() => {
9  console.log('promise 1');
10  process.nextTick(() => console.log('nextTick 3'));
11});
12 
13queueMicrotask(() => console.log('microtask 2'));
14 
15console.log('end');

output1

Command Palette

process.nextTick vs Promise Microtasks