Walk into the interview having already heard the questions.
A full-stack prep book for JavaScript, React, Node.js, MongoDB, system design, DSA and HR rounds. Every chapter ends with the follow-ups interviewers actually ask.
Interviewer asks
How can closures cause memory leaks?
- chapters
- 147
- DSA questions, tracked
- 226
- career roadmaps
- 50
- open source, no sign-up
- Free
Organised around the interview loop
Six rounds, in the order most full-stack loops run. Each one lists what the interviewer is checking and the chapters that cover it.
Backend
APIs, auth, data modelling, and a typed MERN feature end to end.
System design
Trade-offs at scale, out loud, on a whiteboard.
Every chapter reads the same way
Five parts, always in this order, so revising a topic the night before takes minutes. Here is chapter 1, trimmed.
1Definition
Closures
A closure is a function that remembers the variables from the scope it was created in, even after that scope has finished executing.
2Explanation
Every function carries a hidden reference, [[Environment]], to the scope it was defined in. Call it from anywhere later and it can still reach those variables.
3Code
function createCounter() {
let count = 0;
return () => ++count; // closes over count
}
const next = createCounter();
next(); // 1
next(); // 24Real-world use
Express middleware closes over its config: app.use(authMiddleware(config)).
5Likely questions
What’s the output of the classic setTimeout loop?
How can closures cause memory leaks?
Read the full chapterInterviewing somewhere specific?
Product companies and service firms run very different loops. Each page covers that company’s rounds and the questions that come up.
Product companies 12
Usually weighted toward DSA and system design.
Thinking past the next interview?
50 career roadmaps and 1233 topics. Each stage says what to learn and which project proves you learned it.
Change the example. Run it again.
The JavaScript playground runs in a sandboxed frame in your browser. No server, no account, and your code never leaves your machine.
Before you start
Something missing? Open an issue on GitHub
Is this full-stack interview prep really free?
Yes. The entire curriculum, including over 200+ Data Structures & Algorithms questions, system design guides, and React/Node.js cheat sheets, is 100% open-source and free forever.
Which companies are these questions meant for?
Our curriculum is meticulously categorized into FAANG (Google, Amazon, Meta, Microsoft, Oracle) and top Service companies (TCS, Infosys, Wipro, Accenture). We track the exact questions asked in their most recent 2026 hiring cycles.
Do I need to know both React and NestJS?
While the book heavily features React on the frontend and Node.js/NestJS on the backend, the core architectural concepts (System Design, Microservices, Authentication, Database Indexing) apply universally across any technology stack.
What are the career roadmaps?
Stage-by-stage study maps for the roles hiring right now — 50 tracks covering 1233 topics, from AI and ML engineering to data, MLOps, and forward deployed engineering. Each one tells you what to learn, in what order, and what to build to prove it.
Do I need an account, and how is my progress saved?
There is no account and no sign-up. Ticked topics and roadmap progress are stored in your own browser using localStorage, so nothing is uploaded and nothing is tracked. Clearing your browser data resets your progress, and it does not follow you to another device.
Can I run the code examples?
Yes. The JavaScript Playground runs your code directly in your browser inside a sandboxed frame — no server, no account, and your code never leaves your machine. Use it to tweak any example from the book and see the console output immediately.
How do I report an error or contribute?
The whole book is a public GitHub repository. Open an issue for anything that looks wrong or out of date, or send a pull request — corrections, new questions, and better explanations are all welcome.