Train for Real JavaScript Interviews

JavaScript Interview
Questions & Practice.

Practice real JavaScript interview questions, take timed Interview Sprint and know exactly if you're ready.

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93+ core JavaScript questions — free, forever.No card. No trial. No paywall.
252+
Questions
4
Practice modes
40
Topic guides
6
AI tools

AI Answer Evaluator

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Type your answer. Get scored 1–10 with specific gaps — not "great job".

JSPrep Pro · Answer Evaluator
JavaScriptCore
What is a closure in JavaScript, and why is it useful?
Your answer
A closure is when a function has access to variables from its outer scope, even after the outer function has returned. It's useful for data privacy and keeping state in counters.
7/10
Good — room to grow
✓ Correct on scope retention and persistence. Missing the key mechanic — closures work because of lexical scoping. A senior answer would mention the module pattern or React hooks as real-world usage.

⚡ New: Interview Sprint

The fastest way to know if you're ready

A timed mixed-question challenge. Theory + output + debugging. AI judges your answers. One score tells you exactly where you stand.

🎯
Real interview format

Mixed question types under time pressure — exactly how interviews work

🤖
AI scores theory answers

No multiple choice. You explain in your own words, AI grades like a senior engineer

📊
Strengths & weak areas

After each sprint: know exactly which categories to keep drilling

🏆
Shareable score card

Download or tweet your result — challenge your network to beat your score

70pts
Q5 / 1040% complete
7:23
⚡ Active question
💻 OutputCoreType Coercion

What does this print?

console.log([] + [])
console.log([] + {})
console.log({} + [])
Type the expected output...
Check
Skip →
🤖 Previous — AI scored
📖 TheoryClosures

What is a closure in JavaScript?

A closure is a function that remembers variables from its outer scope even after the outer function returns...
8/10 · B+
Good — missing one key detail
✓ Core concept✗ Edge cases
+10 pts
Up next
🐛 Find the bug in this code
📖 Explain the concept in depth
🏆 Sample result
172/200 pts86% accuracy
Strong: Closures · Hoisting · Scope
Review: Event Loop · Promises
📤 Share score
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Four Practice Modes

How real JavaScript interviews test you

Most prep sites are theory-only. Real JavaScript interviews use all four.

📖
✓ Free
Concepts
93 questions

Core JS theory with AI-graded written answers. Not MCQ — you explain it.

ClosuresScopePrototypesEvent Loop
💻
✓ Free
Output Quiz
106 questions

Predict what the console prints. The most common real interview format.

CoercionHoistingAsyncthis
🐛
Debug Lab
28 questions

Find and fix real bugs. AI tells you exactly what you missed.

Async bugsScope issuesLogic errors
🧪
Polyfill Lab
25 questions

Write Array.map, Promise.all and bind from scratch with test feedback.

Array methodsPromisesbind / call

Beyond Questions

A full interview prep ecosystem

Not just a list of Q&As — habits, accountability, and depth.

Question of the Day — Free
One question a day. Answer it. Get AI feedback. Stay ready.

Builds the daily prep habit without overwhelm. Free for everyone — no Pro needed. Track your streak.

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Top Learners This Week
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Yash Maheshwari
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Why devs switch to JSPrep Pro

📖
Theory
Read definitions on MDN
Understand with AI + code examples
💻
Output Questions
Get surprised in interviews
Predict output confidently
🐛
Debug Challenges
Never practiced bug fixing
AI-scored real bug fixing practice
🧪
Polyfill Lab
Skipped polyfills entirely
Write reduce, bind, Promise.all with test feedback

Real developers. Real offers.

They prepped here. They got in.

Not "I liked the UI." — Developers, interviews, outcomes.

"

The questions I practiced were almost identical to what was asked in my interview — something I wouldn’t have prepared on my own. Great platform for targeted prep.

YM
Yogita Munjal
Backend Dev → EasyEcom
"

The AI evaluator is the real thing. It told me I was hand-waving through closures. Fixed it, aced the Bajaj Finser Health round. Worth every rupee.

YM
Yash Maheshwari
React Dev → Bajaj Finserv Health
"

Failed my first Atlassian screen because of the event loop. Spent a week here, went back for round 2, passed. Completely different outcome.

SS
Smridhi Soni
2 YOE → Atlassian

40 Topic Deep-Dives

Every JavaScript concept, interview-ready

Each topic has a mental model, full explanation, cheat sheet, and practice questions. Not just a Q&A list.

JavaScript Memoization Interview Questions
Intermediate4–8 questions
JavaScript Design Patterns Interview Questions
Senior4–8 questions
JavaScript Deep Clone vs Shallow Clone Interview Questions
Intermediate4–8 questions
JavaScript Closure Interview Questions
Intermediate8–12 questions
JavaScript Event Propagation Interview Questions
Intermediate4–8 questions
JavaScript Optional Chaining & Nullish Coalescing
Beginner4–8 questions
See all 40 topics

6 AI Features

Your AI interview coach

Not a chatbot you switch to. AI is inside every question, every answer, every debug.

Answer EvaluatorPRO

Type your answer, get scored 1–10 with specific gaps

AI TutorPRO

Ask follow-ups on any question, get real examples

Code CheckerPRO

AI validates your fix and suggests a cleaner approach

Mock InterviewerPRO

Full back-and-forth with an AI senior engineer

Study PlanPRO

Personalized day-by-day prep from your weak spots

Cheat SheetPRO

36-topic revision cards, printable PDF

Pricing

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  • First 5 polyfill challenges
  • Weekly XP leaderboard
  • Interview Cheat Sheet
  • Deep Dives (in-depth concept explanations)
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