---
title: JavaScript Interview Questions & Answers (2026): Closures, Async & the Event Loop
description: The JavaScript interview questions that get asked in 2026 — closures, hoisting, this, promises, async/await and the event loop — with clear answers and what each one really tests.
url: https://usegreenroom.app/blog/javascript-interview-questions
last_updated: 2026-06-19
---

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Technical

# JavaScript interview questions and answers

June 19, 2026 · 10 min read

![JavaScript interview questions and answers — cover from Greenroom, the AI mock interviewer](/assets/blog/javascript-interview-questions-hero.webp)

JavaScript powers every frontend role and a huge share of backend ones, and its interviews reward understanding the language's quirky core: closures, `this`, asynchronous behavior, and the event loop. These few concepts come up again and again. Here are the **JavaScript interview questions** that actually get asked, with answers. (For frontend-specific topics, see our frontend interview guide.)

## Core JavaScript

- `var` vs `let` vs `const`; hoisting and the temporal dead zone.
- `==` vs `===` and type coercion.
- What is a closure, and a real use case?
- How does `this` work, and how do call/apply/bind change it?
- Primitive vs reference types; pass by value vs reference.

## Asynchronous JavaScript

- Explain the **event loop**, the call stack, and the task/microtask queues.
- Callbacks vs promises vs async/await.
- What is callback hell and how do promises solve it?
- `Promise.all` vs `Promise.race` vs `Promise.allSettled`.

![JavaScript interview topics — closures, hoisting, this, async, event loop](/assets/blog/pool-structured-screen.webp)

JS rounds live and die on closures, 'this', and the event loop — know them cold.

## Functions & objects

- Arrow functions vs regular functions (especially `this` binding).
- Prototypal inheritance and the prototype chain.
- Debouncing vs throttling — and when to use each.
- Higher-order functions; map, filter, reduce.

**The core truth:** JavaScript interviews hinge on a handful of deep concepts — closures, `this`, and the event loop. Candidates who truly understand asynchronous execution stand out instantly, because most people only memorize the syntax of async/await without grasping what's happening underneath.

## How to prepare

Output-prediction and "explain what this does" questions are common, so practise *narrating* code behavior out loud. Greenroom runs spoken technical interviews that follow up on your reasoning and give feedback on clarity. Pair it with our frontend and React guides.

## Frequently asked questions

### What are the most common JavaScript interview questions?

Common JavaScript questions cover var/let/const and hoisting, == vs === and coercion, closures, how 'this' works with call/apply/bind, the event loop and microtask queue, callbacks vs promises vs async/await, prototypal inheritance, arrow vs regular functions, and debouncing vs throttling. Closures, 'this' and asynchronous behavior are the highest-yield topics.

### What is a closure in JavaScript?

A closure is a function that retains access to variables from its outer (enclosing) scope even after that outer function has finished executing. Closures are how JavaScript implements data privacy and stateful functions — for example a counter function that keeps a private count variable that only its returned inner function can read and update.

### How does the JavaScript event loop work?

JavaScript runs on a single thread with a call stack. Asynchronous callbacks wait in queues — the microtask queue (promises) and the macrotask queue (timers, I/O). The event loop continuously checks whether the call stack is empty, then pushes queued callbacks onto it, processing all microtasks before the next macrotask. This is how single-threaded JS handles concurrency.

### How should I prepare for a JavaScript interview?

Focus on the deep core concepts — closures, 'this' binding, prototypal inheritance and especially the event loop and async/await — rather than just syntax, since these separate strong candidates. Practise narrating code behavior and output predictions out loud, ideally with a voice-based mock interview, because these rounds are often live and verbal.

JS interviews hinge on closures, 'this', and the event loop — explained out loud. Greenroom runs spoken technical interviews with feedback on your reasoning. Free to start.