JavaScript Interview Questions & Practice.
Practice real JavaScript interview questions, take timed Interview Sprint and know exactly if you're ready.
93 core JavaScript questions free. No card needed.
Know exactly where you stand
What is a closure in JavaScript, and why is it useful?
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.
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.
Type your answer. Get scored 1 to 10 with specific gaps, not “great job”.
1. How real JavaScript interviews test you
Most prep sites are theory-only. Real JavaScript interviews use all four.
- ConceptsFree93 questionsCore JS theory with AI-graded written answers. Not MCQ, you explain it.ClosuresScopePrototypesEvent Loop
- Output QuizFree111 questionsPredict what the console prints. The most common real interview format.CoercionHoistingAsyncthis
- Debug Lab28 questionsFind and fix real bugs. AI tells you exactly what you missed.Async bugsScope issuesLogic errors
- Polyfill Lab25 questionsWrite Array.map, Promise.all and bind from scratch with test feedback.Array methodsPromisesbind / call
2. 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, and challenge your network to beat your score
What does this print?
console.log([] + [])
console.log([] + {})
console.log({} + [])Skip
What is a closure in JavaScript?
“A closure is a function that remembers variables from its outer scope even after the outer function returns…”
Good, missing one key detail
- Up next
- Find the bug in this code
- Explain the concept in depth
Strong: Closures, Hoisting, Scope
Review: Event Loop, Promises
3. Frontend Developer Roadmap 2026
Stop wondering what to learn next. 112 daily tasks: JS, React, machine coding, DSA, interviews. Progress saved to browser.
- M1, Weeks 1 to 4ClosuresEvent loopPrototypesAsync/awaitPolyfillsJS Mastery
- M2, Weeks 5 to 8FiberAll hooksPerformancePatternsReact 18React Deep Dive
- M3, Weeks 9 to 1230+ components2 projectsDSA sprintGitHub portfolioMachine Coding
- M4, Weeks 13 to 16Mock interviewsSystem designApplicationsNegotiationInterview Mode
4. A full interview prep ecosystem
Not just a list of Q&As: daily habits and depth.
Builds the daily prep habit without overwhelm. Free for everyone, no Pro needed.
Why devs switch to JSPrep Pro
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 QuestionsIntermediate4–8 questions
- JavaScript Design Patterns Interview QuestionsSenior4–8 questions
- JavaScript Deep Clone vs Shallow Clone Interview QuestionsIntermediate4–8 questions
- JavaScript Closure Interview QuestionsIntermediate8–12 questions
- JavaScript Event Propagation Interview QuestionsIntermediate4–8 questions
- JavaScript Optional Chaining & Nullish CoalescingBeginner4–8 questions
Your AI interview coach
Not a chatbot you switch to. AI is inside every question, every answer, every debug.
Type your answer, get scored 1 to 10 with specific gaps
Ask follow-ups on any question, get real examples
AI validates your fix and suggests a cleaner approach
Full back-and-forth with an AI senior engineer
Personalized day-by-day prep from your weak spots
36-topic revision cards, printable PDF
Pricing
Simple. Transparent. Start free with 93 questions and a daily AI-scored question.
- All theory questions
- Interview Sprint, 5-question warmup
- Daily Question of the Day + AI eval
- Interactive practice on the first 5 output + 5 debug questions
- Interactive practice on the first 5 polyfill challenges
- JavaScript and React cheat sheets
- Deep Dives (in-depth concept explanations)
- Everything in Free
- Interview Sprint, unlimited
- Interactive practice on all output, debug and polyfill questions
- Unlimited mastery tracking
- Bookmarks + cloud sync
- Timed quiz / flashcard mode
- AI Tutor on every question
- AI Answer Evaluator
- AI Code Checker
- AI Mock Interviewer
- AI Study Plan generator
- Daily streak tracking
- All future content
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93 questions free, plus a daily AI-scored question. No card needed.
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