1000+ Node JS MCQ Interview Questions

Preparing for Node JS interviews can be intimidating — especially when you're expected to know everything from the event loop to Express internals and security best practices. This course helps you prepare smartly, not just quickly. With a strong focus on MCQ-based interview questions, this course is designed to simulate real interview patterns used by top tech companies.

You’ll cover a wide spectrum of Node JS concepts — from understanding asynchronous behavior and memory management, to working with file systems and creating secure REST APIs. Each question in this course is carefully explained with deep technical insight, so you not only get the right answer but understand the “why” behind it.

We also include common mistakes and traps engineers fall into — such as callback hell, blocking code in event loop, improper error handling, and middleware misuse — so you can avoid them during interviews and on the job.

By the end of this course, you will:

• Be prepared for both junior and mid-level Node JS interviews

• Develop confidence in answering tricky backend questions

• Understand Node internal behavior, not just surface syntax

Whether you’re a student or an industry professional switching stacks, this course is your step-by-step guide to acing Node JS interviews.

Topics Included Are :.

I. Fundamentals of Node and JavaScript (Beginner to Intermediate)

1. Node and its Runtime

Difficulty: Beginner to Intermediate | Questions: 25-30

Event Loop

• Phases order (timers, pending callbacks, idle/prepare, poll, check, close callbacks) - High Priority

• Microtasks vs. Macrotasks execution order - High Priority

• process.nextTick() vs. setImmediate() - High Priority

• Blocking vs. Non-blocking I/O - High Priority

V8 Engine

• Role in Node - Medium Priority

• Just-In-Time (JIT) compilation concept - Medium Priority

• Garbage Collection principles (Mark-and-Sweep, Generational GC) - Low Priority

Asynchronous Nature

• Callback Hell / Pyramid of Doom - Medium Priority

• Promises: Chaining, Promise.all, Promise.race, Promise.any, Promise.allSettled - High Priority

• Async/Await: Syntax, error handling (try...catch) - High Priority

Module System

• CommonJS (require/module.exports) syntax and behavior - High Priority

• ES Modules (import/export) syntax and behavior - High Priority

• Differences and interoperability - Medium Priority

Global Objects

• global vs. window - Medium Priority

• process object: argv, env, exit - Medium Priority

• Buffer: Handling binary data - Medium Priority

Streams

• Types of streams (Readable, Writable, Duplex, Transform) - High Priority

• Piping streams - Medium Priority

• Backpressure mechanism - Medium Priority

EventEmitter

• Creating and using custom event emitters - Medium Priority

• on(), emit(), removeListener() - High Priority

2. Backend Communication Protocols

Difficulty: Intermediate | Questions: 25-30

HTTP Protocols

• HTTP/1.1: Request/response cycle, connection per request - Medium Priority

• HTTP/2: Multiplexing, Server Push, Header Compression (HPACK) - High Priority

• HTTP/3: QUIC protocol, UDP-based - Medium Priority

RESTful APIs

• Principles (Stateless, Uniform Interface, Cacheable) - High Priority

• Idempotency of HTTP methods (GET, PUT, DELETE) - High Priority

• Common HTTP Methods (GET, POST, PUT, PATCH, DELETE) - High Priority

• Status Codes (2xx, 3xx, 4xx, 5xx) - High Priority

• Richardson Maturity Model levels - Low Priority

WebSockets

• Bidirectional communication - High Priority

• Use cases (real-time chat, notifications) - Medium Priority

• Handshake process - Low Priority

GraphQL

• Concepts (single endpoint, query language) - Medium Priority

• Advantages over REST (over-fetching/under-fetching) - High Priority

• Schema Definition Language (SDL) - Low Priority

• Resolvers - Low Priority

gRPC

• Protocol Buffers (serialization) - Medium Priority

• Advantages (performance, strong typing) - High Priority

• IDL-first approach - Medium Priority

• Use cases - Medium Priority

3. Express (Basic to Advanced)

Difficulty: Beginner to Intermediate | Questions: 20-25

Middlewares

• Application-level middleware - High Priority

• Router-level middleware - High Priority

• Error-handling middleware - High Priority

• Custom middleware creation - Medium Priority

• Order of execution (next()) - High Priority

• Common third-party middlewares (body-parser, cors, helmet, morgan) - Medium Priority

Routes

• Defining routes (app get, app post, etc) - High Priority

• Route parameters vs. Query parameters - High Priority

• Chained route handlers - Medium Priority

Status Codes

• Understanding specific codes (2xx, 3xx, 4xx, 5xx) - High Priority

• Appropriate use in API responses - High Priority

Global Catches (Error Handling)

• Centralized error handling middleware - Medium Priority

• Asynchronous error handling strategies - High Priority

• Custom error classes - Low Priority

• Graceful shutdown - Medium Priority

4. ORMs (Object-Relational Mappers)

Difficulty: Intermediate | Questions: 10-12

• Purpose and benefits of ORMs - High Priority

• Basic CRUD operations (Create, Read, Update, Delete) - High Priority

• Schema definition and modeling - Medium Priority

• Associations/Relationships (one-to-one, one-to-many, many-to-many) - High Priority

• Database Migrations (for SQL ORMs) - Medium Priority

5. Zod

Difficulty: Beginner | Questions: 8-10

• Schema validation for data types - High Priority

• Validation of complex structures (objects, arrays) - Medium Priority

• Input validation for API endpoints (body, query, params) - High Priority

• Refinements and transformations - Medium Priority

• Integration with frameworks - Low Priority

II. Databases and Data Management (Intermediate to Advanced)

6. Databases (NoSQL/SQL)

Difficulty: Intermediate | Questions: 10-12

• Relational vs. Non-relational databases: Fundamental differences - High Priority

• Use cases for SQL databases - Medium Priority

• Use cases for NoSQL databases - Medium Priority

• SQL Databases: ACID properties (Atomicity, Consistency, Isolation, Durability) - High Priority

• NoSQL Databases: BASE properties (Basically Available, Soft state, Eventually consistent) - High Priority

• Data Modeling principles for SQL - Medium Priority

• Data Modeling principles for NoSQL - Medium Priority

7. MongoDB and PostgreSQL Deep Dive

Difficulty: Advanced | Questions: 35-40

MongoDB (NoSQL)

• Document-oriented model, JSON-like documents, flexible schema - High Priority

• Indexes: Single-field, compound, text, geospatial, TTL - High Priority

• Aggregation Framework: $match, $group, $project, $lookup, $unwind, $sort - High Priority

• Replication (Replica Sets): Concept, high availability, read scaling - High Priority

• Sharding: Horizontal scaling, sharding keys, chunk migration - Medium Priority

• Multi-document Transactions - Medium Priority

PostgreSQL (SQL)

• Relational model, tables, rows, columns, data types - High Priority

• Advanced SQL queries: Joins (INNER, LEFT, RIGHT, FULL) - High Priority

• Subqueries and Common Table Expressions (CTEs) - Medium Priority

• Window functions - Low Priority

• Indexes: B-tree, Hash, GiST, GIN, when to use which - High Priority

• Transactions and Isolation Levels (Read Committed, Repeatable Read, Serializable) - High Priority

• Table Partitioning - Medium Priority

• Stored Procedures and Functions - Low Priority

• JSONB data type handling - Medium Priority

8. Redis Deep Dive

Difficulty: Advanced | Questions: 20-25

• In-memory data store, single-threaded nature - High Priority

• Data Structures: Strings, Hashes, Lists, Sets, Sorted Sets, Streams, Bitmaps - High Priority

• Use cases: Caching (LRU, TTL) - High Priority

• Session Management - Medium Priority

• Pub/Sub mechanism - Medium Priority

• Rate Limiting - Medium Priority

• Distributed Locks - Medium Priority

• Persistence: RDB snapshotting, AOF (Append-Only File) - High Priority

• Clustering and High Availability: Redis Sentinel, Redis Cluster - High Priority

9. Advanced Database Concepts

Difficulty: Advanced | Questions: 15-20

Indexing

• Importance for query optimization - High Priority

• Trade-offs of indexing (write performance, storage) - High Priority

• Index selection strategies - Medium Priority

Normalization

• Normal forms (1NF, 2NF, 3NF, BCNF) - High Priority

• Impact on data integrity and redundancy - High Priority

Denormalization

• When and why to denormalize - Medium Priority

• Strategies for read performance - Low Priority

III. System Design and Scalability (Advanced)

10. Advanced Backend Communication

Difficulty: Advanced | Questions: 40-50

Message Queues and Pub/Subs

• Purpose: Decoupling services, asynchronous processing, load leveling, fault tolerance, ordered delivery - High Priority

Kafka

• Topics, Partitions, Producers, Consumers, Consumer Groups - High Priority

• Brokers, Zookeeper/Kraft - Medium Priority

• Offsets, Consumer Lag - Medium Priority

• Use cases (log aggregation, real-time data pipelines, event sourcing) - High Priority

RabbitMQ

• AMQP protocol - Low Priority

• Exchanges (direct, fanout, topic, headers), Queues, Bindings - High Priority

• Acknowledgments (ACK/NACK) - Medium Priority

NATS

• High-performance messaging, Pub/Sub, Request/Reply patterns - Medium Priority

• JetStream (persistence, streaming) - Low Priority

Proxies, Load Balancers

• Reverse Proxies vs. Forward Proxies - High Priority

• Load Balancing Algorithms (Round Robin, Least Connections, IP Hash) - High Priority

• Sticky Sessions and their implications - Medium Priority

• Health Checks - Medium Priority

API Gateways

• Purpose and benefits (authentication, rate limiting, logging, routing) - High Priority

• Challenges - Medium Priority

Event-Driven Architecture (EDA)

• Principles (loose coupling, scalability, resilience) - High Priority

• Benefits and drawbacks - High Priority

• Choreography vs. Orchestration - High Priority

11. Microservices Architecture

Difficulty: Advanced | Questions: 15-20

• Principles and benefits (independent deployment, technological diversity, scalability, resilience) - High Priority

• Challenges (distributed transactions, data consistency, debugging) - High Priority

• Service Discovery: Client-side vs. Server-side - High Priority

• API Gateway vs. Direct Communication - Medium Priority

• Database per Service pattern - Medium Priority

• Monolith to Microservices migration strategies (Strangler Fig) - Medium Priority

• Bounded Contexts - Low Priority

12. Microservices Communication Patterns

Difficulty: Advanced | Questions: 20-25

Communication Types

• Synchronous: REST, gRPC (when to use each) - High Priority

• Asynchronous: Message queues, event buses (when to use each) - High Priority

• Choreography vs. Orchestration for workflows - High Priority

Resilience Patterns

• Circuit Breakers - High Priority

• Retries with exponential backoff - Medium Priority

• Timeouts - Medium Priority

• Bulkheads - Low Priority

Distributed Transactions

• Two-Phase Commit (2PC) limitations - High Priority

• Sagas pattern (orchestration-based, choreography-based) - High Priority

13. Common Design Patterns in JavaScript

Difficulty: Intermediate to Advanced | Questions: 15-20

• Singleton pattern - High Priority

• Factory pattern - High Priority

• Observer pattern - High Priority

• Decorator pattern - Medium Priority

• Strategy pattern - Medium Priority

• Module pattern - High Priority

• Revealing Module pattern - Medium Priority

• Constructor pattern - Medium Priority

• Prototype pattern - Medium Priority

• Proxy pattern - Medium Priority

• Understanding use cases in Node - Medium Priority

14. Rate Limiting

Difficulty: Advanced | Questions: 8-10

• Algorithms: Token Bucket, Leaky Bucket, Fixed Window Counter, Sliding Window Log/Counter - High Priority

• Implementation strategies (in-memory, distributed with Redis) - Medium Priority

• Handling bursts - Low Priority

15. Captchas and DDoS Protection

Difficulty: Intermediate | Questions: 10-12

• Types of Captchas (Image, Audio, reCAPTCHA) - Medium Priority

• reCAPTCHA integration principles - Low Priority

• Web Application Firewalls (WAFs) - Medium Priority

• CDN-based DDoS protection - Medium Priority

• Common DDoS attack vectors (SYN flood, HTTP flood, UDP flood) - High Priority

16. Sharding, Replication, Resiliency

Difficulty: Advanced | Questions: 20-25

Sharding

• Horizontal partitioning concept - High Priority

• Sharding keys selection - High Priority

• Consistent hashing - Medium Priority

• Benefits (scalability, performance) - High Priority

• Challenges (rebalancing, cross-shard joins) - Medium Priority

Replication

• Master-Slave, Master-Master architectures - High Priority

• Benefits (high availability, read scaling, disaster recovery) - High Priority

Resiliency

• Redundancy and fault tolerance - High Priority

• Graceful degradation - Medium Priority

• Circuit breakers - High Priority

17. Horizontal and Vertical Scaling

Difficulty: Intermediate | Questions: 8-10

• Differences between horizontal and vertical scaling - High Priority

• When to use each - High Priority

• Advantages and disadvantages - High Priority

• Designing stateless services for horizontal scaling - Medium Priority

• Auto-scaling groups concept - Medium Priority

18. Polling and WebSockets

Difficulty: Intermediate | Questions: 8-10

• When to use Polling vs. WebSockets for real-time updates - High Priority

• Long Polling - High Priority

• Server-Sent Events (SSE) - Medium Priority

• Comparing overheads and use cases - Medium Priority

19. Capacity Estimation

Difficulty: Advanced | Questions: 10-12

• Back-of-the-envelope calculations - Medium Priority

• Key metrics: QPS (Queries Per Second), Throughput, Latency - High Priority

• Estimating storage needs - Medium Priority

• Estimating network bandwidth - Medium Priority

• Estimating CPU/memory requirements - Medium Priority

20. CAP Theorem

Difficulty: Intermediate | Questions: 5-7

• Consistency, Availability, Partition Tolerance definitions - High Priority

• Understanding the trade-offs in distributed systems - High Priority

• Examples of databases prioritizing different aspects - High Priority

21. Testing Node Apps

Difficulty: Intermediate | Questions: 12-15

• Unit testing frameworks (Jest, Mocha/Chai) - High Priority

• Integration testing principles - High Priority

• End-to-End testing tools (Cypress, Playwright) - Medium Priority

• Test Driven Development (TDD) principles - Low Priority

• Mocking and Stubbing - High Priority

• Dependency Injection for testability - Medium Priority

22. WebRTC (Basics)

Difficulty: Intermediate | Questions: 8-10

• Peer-to-peer communication concept - High Priority

• Role of signaling servers - High Priority

• NAT traversal (STUN/TURN servers) - High Priority

• Use cases (video conferencing, real-time data sharing) - Medium Priority

IV. General Backend Concepts (Intermediate to Advanced)

23. MonoRepos, Turborepo

Difficulty: Intermediate | Questions: 8-10

• Advantages and disadvantages of monorepos - High Priority

• Benefits like shared code, simplified dependency management - High Priority

• Tools for monorepo management (Nx, Lerna, Turborepo) - Medium Priority

• Faster builds and caching (Turborepo specific) - Low Priority

24. Serverless Backends

Difficulty: Intermediate | Questions: 12-15

• FaaS (Function as a Service) concept - High Priority

• Benefits (pay-per-execution, auto-scaling) - High Priority

• Drawbacks (cold starts, vendor lock-in, debugging) - High Priority

• Event sources for serverless functions - High Priority

• API Gateway integration - Medium Priority

• Managing state in serverless architectures - Low Priority

• Serverless Framework - Low Priority

25. OpenAPI Spec (Swagger)

Difficulty: Intermediate | Questions: 5-7

• Defining RESTful APIs using OpenAPI specification - High Priority

• Generating documentation - Medium Priority

• Client code generation from spec - Medium Priority

26. Autogenerated Clients

Difficulty: Intermediate | Questions: 3-5

• Benefits of generating client-side code from API specifications - High Priority

• Ensuring consistency between client and server - Medium Priority

• Reducing manual errors - Medium Priority

27. Authentication Using External Libraries

Difficulty: Intermediate | Questions: 15-20

• OAuth 2.0: Authorization Code Flow, Client Credentials Flow - High Priority

• OpenID Connect: Authentication layer on OAuth 2.0 - High Priority

• JWT (JSON Web Tokens): Structure, signature verification, common claims - High Priority

• Passport strategies - Medium Priority

• Session management vs. Token-based authentication - High Priority

• Refresh tokens and access tokens - High Priority

28. Scaling Node, Performance Benchmarks

Difficulty: Intermediate to Advanced | Questions: 10-12

• Node cluster module for multi-core utilization - High Priority

• PM2 (process manager for Node.) - High Priority

• Worker threads for CPU-bound tasks - High Priority

• Profiling Node applications (CPU, memory) - Medium Priority

• Tools for benchmarking (Apache Bench, wrk) - Medium Priority

• Identifying performance bottlenecks - High Priority

29. Deploying NPM Packages

Difficulty: Beginner | Questions: 6-8

• Semantic Versioning (SemVer) rules - High Priority

• Publishing packages to npm registry - Medium Priority

• Private npm packages - Low Priority

• package-lock json vs package json - High Priority

V. DevOps and Cloud Deployment (Intermediate to Advanced)

30. Basic DevOps

Difficulty: Intermediate | Questions: 30-35

Docker End to End

• Dockerfile creation and best practices (multi-stage builds) - High Priority

• Docker Compose for multi-container apps - High Priority

• Images vs. Containers - High Priority

• Volumes for data persistence - High Priority

• Networking for containers - High Priority

• Port mapping - High Priority

Deploying to AWS Servers

• EC2 instances (launching, connecting) - Medium Priority

• Security groups configuration - High Priority

• SSH access - Medium Priority

Newer Clouds (Fly io/Remix)

• Understanding their advantages (e.g., global distribution, simpler CI/CD) - Low Priority

• Basic deployment flow - Low Priority

Nginx and Reverse Proxies

• Role as a reverse proxy - High Priority

• Configuration for load balancing - High Priority

• SSL termination - High Priority

• Static file serving - Medium Priority

• Caching - Medium Priority

31. Advanced DevOps

Difficulty: Advanced | Questions: 120-150

Docker Deep Dive

• Containerization best practices (non-root user, minimal images, health checks) - High Priority

• Troubleshooting containers - Medium Priority

Container Orchestration, Docker Swarm

• Basic concepts of orchestration - High Priority

• Docker Swarm features (services, stacks, nodes, routing mesh) - Medium Priority

Kubernetes

• Core Concepts: Pods, Deployments, Services (ClusterIP, NodePort, LoadBalancer), Namespaces, ReplicaSets, DaemonSets, StatefulSets - High Priority

• Controllers, kube-apiserver, etcd, kube-scheduler, kubelet - High Priority

• kubectl commands for deployment, scaling, logging, debugging - High Priority

• Ingress Controllers - High Priority

• Helm charts as package manager - Medium Priority

• Networking in Kubernetes (CNI, Service discovery) - High Priority

• Self-healing and auto-scaling (HPA, Cluster Autoscaler) - High Priority

CI/CD (Continuous Integration/Continuous Deployment)

• Principles and benefits - High Priority

• Common tools (Jenkins, GitLab CI/CD, GitHub Actions, AWS CodePipeline/CodeBuild) - Medium Priority

• Automated testing in pipelines - High Priority

• Deployment strategies (Blue/Green, Canary, Rolling updates) - High Priority

Monitoring Systems

• Three pillars of observability: Logs, Metrics, Traces - High Priority

• Alerting strategies and incident response - Medium Priority

• Distributed tracing (OpenTelemetry, Jaeger) - High Priority

Prometheus, Grafana

• Prometheus: Metrics collection, exporters, PromQL - High Priority

• Grafana: Dashboarding, visualizations, alerting - High Priority

NewRelic (Paid Service)

• Understanding APM (Application Performance Monitoring) - High Priority

• End-to-end transaction tracing - Medium Priority

• Error tracking and infrastructure monitoring - Medium Priority

Serverless Deep Dive

• Design patterns for serverless (fan-out, saga, choke point) - Medium Priority

• Cold starts mitigation strategies - High Priority

• Serverless Framework for deployment - Low Priority

• Event-driven architecture in serverless context - High Priority

AWS Constructs

• EC2: Instances, AMIs, security groups, EBS, Auto Scaling - High Priority

• S3: Object storage, static website hosting, versioning, lifecycle policies - High Priority

• CDNs (CloudFront): Caching, global distribution, WAF integration - High Priority

• Load Balancers (ALB, NLB): AWS-specific implementations - High Priority

• EKS: Managed Kubernetes service - High Priority

• RDS: Managed SQL, Multi-AZ, Read Replicas - High Priority

• DynamoDB: Managed key-value, consistency models, DAX - High Priority

• VPC: Networking (Subnets, Route Tables, Internet Gateways, NAT Gateways) - High Priority

• IAM: Roles, policies, users, groups, least privilege - High Priority

• CloudWatch: Monitoring and logging for AWS - High Priority

• CloudFormation/Terraform (Infrastructure as Code) - High Priority

Summary

Total Estimated Granular Points: 550-700+ concepts