Top JavaScript Interview Questions 2026

Updated today · By SkillExchange Team

1,152

Open Positions

$144,515

Median Salary

18

Questions

Preparing for JavaScript interview questions is crucial if you're aiming for JavaScript developer jobs, especially with 1152 openings listed right now on major job boards. Whether you're eyeing entry level JavaScript jobs, remote JavaScript developer jobs, or senior roles at companies like Carbonhealth, Palantir Technologies, or Sitetracker, nailing these interviews can land you a spot with a median JavaScript developer salary of $144,515 USD, ranging from $64,723 to $223,176. In 2026, hiring javascript developers focuses on practical skills over rote memorization, so understanding real-world scenarios is key.

The best way to learn JavaScript and stand out in a javascript coding test is through a solid javascript roadmap: master fundamentals, dive into modern ES6+ features, tackle asynchronous programming, and build projects. If you're from a javascript bootcamp or pursuing javascript certification, expect questions that test problem-solving in contexts like building scalable web apps or optimizing performance for remote JavaScript jobs. Interviewers at top firms want developers who can handle JavaScript developer job descriptions involving React, Node.js, or full-stack work, so practice explaining your code clearly.

Is javascript worth learning? Absolutely, with booming demand for javascript freelance jobs and JavaScript developer remote positions. This guide covers 18 curated javascript interview questions across beginner, intermediate, and advanced levels, complete with sample answers and tips. Use it to prep efficiently, avoid pitfalls, and boost your chances for those high-paying gigs. Let's dive in and get you interview-ready.

beginner Questions

What are the different data types in JavaScript? Explain primitive vs reference types.

beginner
JavaScript has seven primitive types: undefined, null, boolean, number, bigint, string, and symbol. Reference types include Object (which covers arrays, functions, dates, etc.). Primitives are immutable and passed by value; reference types are mutable and passed by reference. For example, let a = 5; let b = a; b = 10; doesn't change a, but with objects, let obj1 = {x:1}; let obj2 = obj1; obj2.x=2; changes obj1 too.
Tip: Always mention BigInt for modern interviews; it's key for 2026 javascript developer jobs handling large numbers.

Explain let, const, and var with examples.

beginner
var is function-scoped, hoisted, and can be redeclared. let and const are block-scoped, hoisted but not initialized (Temporal Dead Zone). const can't be reassigned but mutable if object. Example: 
var a = 1;
let b = 2;
const c = 3;
if(true){ var a=10; let b=20; const c=30; } // a=10, b=2, c=3
Tip: Stress block scoping; common in javascript coding test to trip up var users.

What is hoisting in JavaScript?

beginner
Hoisting moves declarations to the top of their scope before execution. Only declarations hoist, not initializations. var hoists with undefined; let/const hoist but throw ReferenceError in TDZ. Example: 
console.log(x); // undefined
var x = 5;
Tip: Use this to explain why 'use strict' and modern practices avoid var for hiring javascript developers.

How do you check if a variable is an array?

beginner
Best: Array.isArray(arr). Alternatives: arr instanceof Array (fails cross-frame), Object.prototype.toString.call(arr) === '[object Array]', or arr.constructor === Array. Array.isArray is reliable and standard.
Tip: Array.isArray is the go-to for javascript interview questions; mention edge cases like iframes.

What is the difference between == and ===?

beginner
== coerces types (e.g., '5' == 5 is true), === checks value and type (false). Always use === to avoid bugs. NaN === NaN is false; use Number.isNaN() or isNaN().
Tip: Relate to real bugs in production code; key for entry level JavaScript jobs.

Explain this keyword in different contexts.

beginner
this refers to execution context. Global: window. Object method: object. Constructor: new instance. Arrow: lexical (parent). Event handler: target. Call/apply/bind: specified. Example: const obj = {m: function(){return this;}}; obj.m() === obj.
Tip: Practice with arrows vs regulars; frequent in javascript bootcamp assessments.

intermediate Questions

What are closures? Provide an example.

intermediate
Closure is a function accessing its outer scope's variables even after outer returns. Example: 
function outer(x) {
  return function inner(y) {
    return x + y;
  };
}
const add5 = outer(5); console.log(add5(3)); // 8
Used for data privacy, modules.
Tip: Link to module patterns; essential for javascript roadmap beyond basics.

Explain promises and how to use async/await.

intermediate
Promises represent eventual completion/failure. Chain with .then/.catch. Async/await is syntactic sugar: async function fetchData(){ try{ const res = await fetch(url); return res.json(); } catch(e){...} }. Handles async like sync, cleaner than chains.
Tip: Compare to callbacks; show error handling for remote javascript jobs APIs.

What is event delegation?

intermediate
Attach one listener to parent, handle events on children via event.target. Efficient for dynamic lists. Example: 
document.querySelector('ul').addEventListener('click', (e) => {
  if(e.target.tagName === 'LI') { e.target.style.color = 'red'; }
});
Tip: Great for performance in large apps; mention in JavaScript developer job description talks.

Differentiate preventDefault() from stopPropagation().

intermediate
preventDefault() stops default browser action (e.g., link navigation). stopPropagation() stops event bubbling up. Use both if needed: e.preventDefault(); e.stopPropagation();.
Tip: Real-world: forms in SPAs; common in javascript coding test.

What is prototypal inheritance?

intermediate
Objects inherit from prototypes. obj.__proto__ === Constructor.prototype. Chain via Object.create() or classes. Example: 
function Animal(){}
Animal.prototype.speak = function(){...};
const dog = new Animal();
Tip: ES6 classes are sugar; understand proto for advanced javascript interview questions.

How does map(), filter(), reduce() work?

intermediate
map() transforms array. filter() selects. reduce() aggregates. Example reduce sum: 
[1,2,3].reduce((acc, curr) => acc + curr, 0); // 6
Don't mutate original.
Tip: Practice chaining; optimizes for javascript freelance jobs.

advanced Questions

What is a curry function? Implement one.

advanced
Currying transforms f(a,b,c) to f(a)(b)(c). Example: 
function curry(f) {
  return function(a) {
    return function(b) {
      return f(a,b);
    };
  };
}
const sum = curry((a,b)=>a+b);
Useful for partial application.
Tip: Relate to functional programming; hot for 2026 JavaScript jobs remote.

Explain the event loop and microtasks vs macrotasks.

advanced
Event loop processes call stack, then microtasks (Promise.then), then macrotasks (setTimeout). Stack: sync code. Micro before macro. Example: console.log(1); setTimeout(()=>console.log(2)); Promise.resolve().then(()=>console.log(3)); // 1,3,2
Tip: Crucial for async debugging; test in javascript coding test.

What are WeakMap and WeakSet? When to use?

advanced
WeakMap/WeakSet hold weak references to objects (GC eligible). Keys/objects auto-removed. Use for caches, avoiding memory leaks. const wm = new WeakMap(); wm.set(obj, value); No iteration.
Tip: Memory management key for scalable apps at Palantir-like firms.

Implement debounce function.

advanced
function debounce(fn, delay) {
  let timer;
  return function(...args) {
    clearTimeout(timer);
    timer = setTimeout(() => fn.apply(this, args), delay);
  };
}
For search inputs, scroll events.
Tip: Real-world UI perf; mention in hiring javascript developers convos.

What is the Temporal Dead Zone?

advanced
TDZ: period where let/const hoisted but accessing throws ReferenceError until declaration. console.log(a); let a=1; errors. Avoids var-like bugs.
Tip: Pairs with hoisting; advanced for javascript certification.

Optimize this loop for 1M items: find sum of even numbers.

advanced
Use reduce(): arr.reduce((sum, num) => num%2===0 ? sum+num : sum, 0). Or forEach with early continue. Avoid nested loops. For huge arrays, Web Workers.
Tip: Perf matters for javascript developer salary at scale; discuss Big O.

Preparation Tips

1

Build 3-5 projects on GitHub following a javascript roadmap, like a todo app with async APIs, to showcase for JavaScript developer jobs.

2

Practice live coding on platforms like LeetCode or HackerRank for javascript coding test prep; time yourself under 45 mins.

3

Mock interview with peers focusing on explaining this, closures, event loop - verbal skills win remote JavaScript developer jobs.

4

Review modern features: optional chaining, nullish coalescing, private fields (#) for 2026 javascript bootcamp edge.

5

Tailor resume to JavaScript developer job description keywords; highlight remote experience for JavaScript jobs remote.

Common Mistakes to Avoid

Using var instead of let/const; screams outdated skills to hiring javascript developers.

Confusing promise chains with async/await; practice converting to show fluency.

Forgetting Array.isArray() and using typeof; fails edge cases in interviews.

Not handling this in callbacks; use arrows or bind.

Overlooking event loop order; microtasks trip up many in advanced javascript interview questions.

Related Skills

React.jsNode.jsTypeScriptHTML/CSSWeb APIs (Fetch, DOM)Performance OptimizationTesting (Jest)Build Tools (Webpack, Vite)

Top Companies Hiring JavaScript Professionals

Carbonhealth (8)Employee Referrals (5)Raya (5)NeueHealth (5)Innocraft (5)Palantir Technologies (4)Sitetracker (4)Catena Media (4)WebPresented (4)Job Corp (4)

Explore More About JavaScript

JavaScript Salary Guide
Compensation data for JavaScript roles
JavaScript Job Market
Hiring trends and demand for JavaScript

Frequently Asked Questions

What is the average JavaScript developer salary in 2026?

Median is $144,515 USD, ranging $64,723-$223,176. Remote javascript jobs often pay higher at top firms like Palantir.

How to prepare for javascript coding test?

Practice medium LeetCode JS problems, focus on arrays/objects, optimize time/space. Simulate with timer.

Are remote JavaScript developer jobs common?

Yes, with 1152 openings, many at Carbonhealth, NeueHealth. Skills in React/Node key.

Is javascript worth learning in 2026?

Definitely; demand high for javascript freelance jobs, certifications boost entry level JavaScript jobs.

Best way to learn javascript for interviews?

Follow javascript roadmap: MDN docs, freeCodeCamp, then projects. Get javascript certification for credibility.

Ready to take the next step?

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