Microtask
- Node.js course
- Expert
- Lesson 14/47
- 5 min
Learn microtasks and nextTick.
Microtask
Microtasks are small jobs that run between event loop phases. There are two kinds: process.nextTick and Promise callbacks. nextTick always runs before Promises.
A microtaskOrder(tasks) function models this priority: it turns the array ['nextTick', 'promise'] into the string 'nextTick -> promise'. In real Node.js the microtask queue is drained after each phase; the nextTick queue first, then the promise queue. So if process.nextTick(() => ...) and Promise.resolve().then(() => ...) are used together, nextTick runs first. The output is nextTick -> promise; this order always holds.
nextTick priority
We can model the microtask order with a function. microtaskOrder(['nextTick', 'promise']) returns 'nextTick -> promise'. This shows with a fixed string that nextTick always runs first.
The function is simple: return tasks.join(' -> '). The tasks array is already in the right order (nextTick first). The output is nextTick -> promise. In real Node.js this order comes from how the microtask queue is drained: the nextTick queue is fully emptied, then the promise queue. This model visualizes the order with a deterministic string; no timer uncertainty. The fact that nextTick runs before Promise is thus pinned down.
Practice Write the microtask order
Write function microtaskOrder(tasks). Return tasks.join(' -> '). Print console.log(microtaskOrder(['nextTick', 'promise'])).
Starter code
// Write a microtaskOrder function
// Join the task array with ' -> '
// Call with ['nextTick', 'promise'], print
// write hereSample solution
function microtaskOrder(tasks) {
return tasks.join(' -> ');
}
console.log(microtaskOrder(['nextTick', 'promise']));Expected output
nextTick -> promise
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Match each concept to its description
| Term | Meaning |
|---|---|
process.nextTick |
Microtask that runs first |
Promise.then |
Microtask that runs after nextTick |
Microtask |
Runs between phases |
Phase |
Event loop step |
2 Complete the join call
return tasks.____(' -> ');return tasks.join(' -> ');Explanation: join combines the array into a string.
3 If nextTick and Promise are used together, which runs first?
process.nextTick(() => {});
Promise.resolve().then(() => {});- At the same time
- Rastgele
- Promise
- nextTick Correct answer
Explanation: nextTick always runs before Promise.