What is the run-to-completion?

A job finishes before any other job runs.

What is the after each task?

Microtask queue drained completely, then possible render.

What is the promise executor?

Runs synchronously inside new Promise.

What is the at await?

Control returns to the caller; continuation is a microtask.

What is the timer delay?

A minimum threshold, not an exact time.

What is the node queue order?

nextTick, then promise microtasks, then macrotasks.

What is the inside an I/O callback?

setImmediate always before setTimeout(0).

Asynchronous Programming13% of the exam

Event loop, microtasks and timers

How the call stack, task queue and microtask queue decide the order of synchronous code, promise callbacks, await continuations, queueMicrotask and setTimeout; why timer delays are minimums and long work blocks the page; how Node.js orders process.nextTick, promises, setImmediate and timers; and why errors thrown in timers escape try...catch.

Official exam objective

Given a scenario, use event loop and event monitor or determine loop outcomes.

~6 min read · 18 practice questions · updated Oct 16, 2026

What the exam expects

Predict the log order of synchronous code, promise callbacks, await continuations, queueMicrotask and setTimeout/setInterval callbacks.
Explain why a timer's delay is a minimum, why long synchronous work freezes a page, and how chunking or a Web Worker fixes it.
Order Node.js callbacks: process.nextTick, promise microtasks, setImmediate and timers, inside and outside an I/O callback.
Explain why an error thrown in a timer callback escapes the try...catch that scheduled it, and use an event monitor to watch events as they fire.
Key terms: call stack (frames of the code running now); task (macrotask: a script, timer callback or dispatched event, run one per loop iteration); microtask (promise reaction, await continuation or queueMicrotask callback, run when the stack empties); run-to-completion (a running job is never interrupted); tick (Node's term for one call back into JavaScript).

Key facts

Fact	Detail	Source
Run-to-completion	A job finishes before any other job runs	Execution model (opens in a new tab)
After each task	Microtask queue drained completely, then possible render	Microtask guide (opens in a new tab)
`queueMicrotask` vs `then`	Same microtask queue, FIFO	Microtask guide (opens in a new tab)
Promise executor	Runs synchronously inside `new Promise`	Promise() constructor (opens in a new tab)
At `await`	Control returns to the caller; continuation is a microtask	await (opens in a new tab)
Timer delay	A minimum threshold, not an exact time	The Node.js Event Loop (opens in a new tab)
Node queue order	nextTick, then promise microtasks, then macrotasks	Understanding setImmediate() (opens in a new tab)
Inside an I/O callback	`setImmediate` always before `setTimeout(0)`	The Node.js Event Loop (opens in a new tab)
Recursive `nextTick`	Starves I/O	The Node.js Event Loop (opens in a new tab)

Run-to-completion

Detail: A job finishes before any other job runs
Source: Execution model (opens in a new tab)

After each task

Detail: Microtask queue drained completely, then possible render
Source: Microtask guide (opens in a new tab)

queueMicrotask vs then

Detail: Same microtask queue, FIFO
Source: Microtask guide (opens in a new tab)

Promise executor

Detail: Runs synchronously inside new Promise
Source: Promise() constructor (opens in a new tab)

At await

Detail: Control returns to the caller; continuation is a microtask
Source: await (opens in a new tab)

Timer delay

Detail: A minimum threshold, not an exact time
Source: The Node.js Event Loop (opens in a new tab)

Node queue order

Detail: nextTick, then promise microtasks, then macrotasks
Source: Understanding setImmediate() (opens in a new tab)

Inside an I/O callback

Detail: setImmediate always before setTimeout(0)
Source: The Node.js Event Loop (opens in a new tab)

Recursive nextTick

Detail: Starves I/O
Source: The Node.js Event Loop (opens in a new tab)

Sources for this section (6)

Check yourself

Why does a promise callback queued after `setTimeout(fn, 0)` still log first?
When does code after `await null` run?
Why does a 100 ms timer fire late when a long loop is running?
Which Node API should schedule the next chunk of a long job so requests are still served?

The questions are free to read. Answers with their sources and self-grading are included with the pack.

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What the exam expects

Key facts

Check yourself

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