MERN INTERVIW

🔹 MERN Stack Interview Questions (3 Years Experience)
🟢 BASIC LEVEL (Foundation Clear Hona Chahiye)
MERN Basics
MERN stack kya hota hai?

MongoDB, Express, React, Node.js ka role kya hai?

Monolithic vs Microservices?

REST API kya hoti hai?

HTTP methods explain kare (GET, POST, PUT, PATCH, DELETE)

HTTP Status codes (200, 201, 400, 401, 403, 404, 500)

JSON kya hota hai aur kyun use hota hai?

Client-server architecture kya hoti hai?

MVC architecture explain karo

🟢 JavaScript Basics
var, let, const difference

Hoisting kya hota hai?

Closure kya hota hai?

== vs ===

Shallow copy vs Deep copy

map, filter, reduce

Arrow function vs normal function

Event loop kya hai?

Synchronous vs Asynchronous JS

🟢 Node.js Basics
Node.js kya hai?

Node.js single threaded kyun hai?

Event-driven architecture kya hoti hai?

npm kya hai?

package.json ka role

Middleware kya hota hai?

require vs import

Environment variables kya hote hain?

🟢 Express.js Basics
Express kya hai?

Routing kya hoti hai?

Middleware types

req, res, next

Error handling kaise karte ho Express me?

CORS kya hota hai?

🟢 MongoDB Basics
NoSQL kya hota hai?

MongoDB vs SQL

Collection, Document kya hote hain?

_id kya hota hai?

Schema kya hota hai (Mongoose)?

find, findOne, insertOne, updateOne, deleteOne

🟡 INTERMEDIATE LEVEL (Real Project Knowledge)
🔹 Node.js / Express
Middleware ka real use case batao

Authentication vs Authorization

JWT kya hota hai?

JWT flow explain karo

Refresh token kya hota hai?

bcrypt kya hai?

Rate limiting kya hota hai?

File upload kaise handle karte ho?

Logging kaise implement karte ho?

API versioning kya hoti hai?

🔹 MongoDB / Database
Index kya hota hai?

Compound index kya hota hai?

Aggregation pipeline explain karo

$lookup kya hota hai?

Pagination kaise implement karte ho?

Transactions MongoDB me kaise kaam karti hain?

Normalization vs Denormalization

MongoDB performance optimize kaise karte ho?

🔹 React (Frontend)
React kya hai?

SPA kya hoti hai?

Virtual DOM kya hota hai?

Props vs State

Controlled vs Uncontrolled components

Hooks kya hote hain?

useState, useEffect

Dependency array ka role

useMemo, useCallback

Context API kya hai?

Redux vs Context API

React Router kya karta hai?

Lazy loading kya hoti hai?

Error boundary kya hota hai?

🔴 ADVANCED LEVEL (3+ Years Real Experience)
🔥 System & Architecture
Large scale MERN app ka architecture explain karo

Monorepo vs Multi repo

Microservices vs Monolith

API Gateway kya hota hai?

Load balancing kya hota hai?

Horizontal vs Vertical scaling

Stateless vs Stateful API

WebSocket vs REST

Kafka / Queue ka use kab karte ho?

🔥 Node.js Advanced
Cluster module kya hai?

Worker threads kya hote hain?

Streams kya hote hain?

Backpressure kya hota hai?

Memory leak kaise detect karte ho?

Process vs Thread

Child process kya hota hai?

Graceful shutdown kaise implement karte ho?

🔥 Security
XSS kya hota hai?

CSRF kya hota hai?

SQL / NoSQL injection

Password hashing best practices

Helmet kya karta hai?

HTTPS kyun important hai?

OAuth kya hota hai?

Role Based Access Control (RBAC)

🔥 Performance & Optimization
React performance optimize kaise karte ho?

Backend caching kaise karte ho? (Redis)

DB query optimization

CDN kya hota hai?

Debouncing & Throttling

🔥 Testing & DevOps
Unit test vs Integration test

Jest kya hai?

Supertest kya hai?

CI/CD kya hota hai?

Docker kya hota hai?

Docker Compose kya karta hai?

Environment-based config kaise manage karte ho?

Logging & Monitoring tools

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