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Top NodeJS Interview Questions

Curated NodeJS interview questions and answers across difficulty levels.

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NodeJS Interview Questions & Answers

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Welcome to our comprehensive collection of NodeJS interview questions and answers. This page contains expertly curated interview questions covering all aspects of NodeJS, from fundamental concepts to advanced topics. Whether you're preparing for an entry-level position or a senior role, you'll find questions tailored to your experience level.

Our NodeJS interview questions are designed to help you:

  • Understand core concepts and best practices in NodeJS
  • Prepare for technical interviews at all experience levels
  • Master both theoretical knowledge and practical application
  • Build confidence for your next NodeJS interview

Each question includes detailed answers and explanations to help you understand not just what the answer is, but why it's correct. We cover topics ranging from basic NodeJS concepts to advanced scenarios that you might encounter in senior-level interviews.

Use the filters below to find questions by difficulty level (Entry, Junior, Mid, Senior, Expert) or focus specifically on code challenges. Each question is carefully crafted to reflect real-world interview scenarios you'll encounter at top tech companies, startups, and MNCs.

Questions

150 questions
Q1:

What is Node.js?

Entry

Answer

Node.js is a runtime environment that allows JavaScript to run outside the browser, mainly used for backend development.
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Q2:

Why was Node.js created?

Entry

Answer

Node.js was created to handle a large number of concurrent requests efficiently using a non-blocking architecture.
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Q3:

What is the V8 engine in Node.js?

Entry

Answer

The V8 engine is Google’s JavaScript engine that compiles JavaScript into fast machine code, helping Node achieve high speed.
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Q4:

What is the event loop in Node.js?

Entry

Answer

The event loop manages asynchronous operations and ensures Node remains responsive without blocking.
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Q5:

What is single-threaded architecture?

Entry

Answer

Node uses one main thread to execute JavaScript while delegating heavy tasks to background workers.
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Q6:

What is npm?

Entry

Answer

npm is Node’s package manager used to install and manage external libraries.
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Q7:

What is a package.json file?

Entry

Answer

A metadata file that stores project details, dependencies, scripts, and configuration.
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Q8:

What are dependencies and devDependencies?

Entry

Answer

Dependencies are required at runtime; devDependencies are used only during development.
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Q9:

What is a callback function?

Entry

Answer

A callback is a function passed as an argument to execute after an asynchronous task finishes.
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Q10:

What is a module in Node.js?

Entry

Answer

A module is a separate file containing reusable code that can be imported into other files.
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Q11:

What is CommonJS?

Entry

Answer

CommonJS is Node’s module system using module.exports and require for import and export.
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Q12:

What is the fs module used for?

Entry

Answer

The fs module provides APIs to create, read, write, and modify files.
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Q13:

What is the path module used for?

Entry

Answer

The path module works with file and directory paths in a cross-platform way.
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Q14:

What is the os module?

Entry

Answer

The os module provides system-level information such as CPU details, memory, and operating system.
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Q15:

What is a buffer in Node.js?

Entry

Answer

A buffer stores binary data in memory, useful for streams, files, and network operations.
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Q16:

What is a stream in Node.js?

Entry

Answer

A stream handles data in chunks, enabling efficient reading and writing without loading full data.
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Q17:

What is server-side JavaScript?

Entry

Answer

It refers to writing backend logic in JavaScript that runs on the server instead of the browser.
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Q18:

What is the http module used for?

Entry

Answer

The http module allows creation of HTTP servers and handling incoming requests.
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Q19:

What is middleware?

Entry

Answer

Middleware functions run between a request and response for tasks like parsing, logging, or validation.
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Q20:

What is Express.js?

Entry

Answer

Express.js is a lightweight web framework for Node that simplifies routing, middleware, and server creation.
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Q21:

What is routing in Node and Express?

Entry

Answer

Routing determines what happens when a specific URL and HTTP method are accessed.
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Q22:

What is JSON in Node.js?

Entry

Answer

JSON is a lightweight data format used for configuration, APIs, and storing structured data.
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Q23:

What is an API endpoint?

Entry

Answer

An API endpoint is a URL where clients send requests and receive responses.
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Q24:

What is an environment variable?

Entry

Answer

Environment variables store external configuration such as API keys or database URLs.
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Q25:

What is process.env?

Entry

Answer

process.env is a built-in object providing access to environment variables.
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Q26:

What is nodemon?

Entry

Answer

Nodemon automatically restarts a Node application when file changes are detected.
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Q27:

What is asynchronous programming in Node?

Entry

Answer

Asynchronous programming allows Node to run tasks without waiting, improving scalability.
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Q28:

What is synchronous programming?

Entry

Answer

Execution happens step-by-step, blocking the thread until each operation completes.
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Q29:

What is an error-first callback?

Entry

Answer

A callback pattern where the first argument is the error and the second is the result.
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Q30:

Difference between console.log and return?

Entry

Answer

console.log prints output to the console; return sends a value back from a function to its caller.
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Q31:

What is the difference between synchronous and asynchronous file operations in Node.js?

Junior

Answer

Synchronous operations block the event loop until the task completes. Asynchronous operations allow Node to continue handling other requests while the file task runs in the background. Async is preferred to avoid blocking.
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Q32:

What is the role of the event emitter?

Junior

Answer

Event emitters allow modules to emit events and let other parts of the app listen and react. It supports decoupled communication between components.
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Q33:

How does Node.js handle concurrency if it is single-threaded?

Junior

Answer

Node uses the event loop and worker threads behind the scenes. The main thread handles requests while heavy operations run in worker threads.
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Q34:

What is middleware chaining in Express.js?

Junior

Answer

Middleware chaining passes control from one middleware to another using next(), building a request pipeline for logging, parsing, authentication, etc.
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Q35:

What is CORS and why is it needed?

Junior

Answer

CORS is a browser security rule restricting cross-domain requests. Node must configure CORS to allow approved domains to access APIs.
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Q36:

What is the difference between PUT and PATCH?

Junior

Answer

PUT replaces the entire resource, while PATCH updates only specific fields.
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Q37:

What is the purpose of Express.js router?

Junior

Answer

Routers organize routes into modules, improving structure and maintainability.
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Q38:

How does Node.js handle errors in asynchronous code?

Junior

Answer

Callbacks use error-first pattern. Async/await uses try/catch or .catch() with promises.
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Q39:

What is a promise in Node.js?

Junior

Answer

A promise represents a future value and helps avoid callback nesting with cleaner chaining.
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Q40:

What is async/await and why is it useful?

Junior

Answer

async/await is syntax built on promises that makes asynchronous code look synchronous and easier to read.
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Q41:

What is the purpose of the cluster module in Node.js?

Junior

Answer

Cluster creates multiple Node processes to use all CPU cores, improving performance.
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Q42:

What is rate limiting in Node.js?

Junior

Answer

Rate limiting restricts how many requests a client can make in a given time to prevent abuse and overload.
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Q43:

What are HTTP status codes and why are they important?

Junior

Answer

Status codes indicate if a request succeeded or failed and help clients understand the response.
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Q44:

What is streaming in Node.js?

Junior

Answer

Streaming processes data in chunks instead of loading it fully in memory. Useful for large files and real-time data.
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Q45:

What is a template engine in Node.js?

Junior

Answer

A template engine creates dynamic HTML using variables. Examples: EJS, Pug, Handlebars.
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Q46:

What is JSON Web Token (JWT)?

Junior

Answer

JWT is a compact token format for authentication, storing encoded user info verified using a secret or key.
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Q47:

What is the difference between global and local npm installation?

Junior

Answer

Global installs work everywhere; local installs stay inside a project folder.
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Q48:

What is nodemailer and where is it used?

Junior

Answer

Nodemailer sends emails from Node apps, such as welcome emails or password resets.
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Q49:

What is dotenv and why is it used?

Junior

Answer

dotenv loads environment variables from a .env file, keeping secrets out of source code.
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Q50:

What is body parsing in Express.js?

Junior

Answer

Body parsing converts request payloads to usable objects. express.json() handles JSON bodies.
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Q51:

What is morgan in Node.js?

Junior

Answer

Morgan is a logging middleware that records request details.
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Q52:

How does Node.js handle database connections?

Junior

Answer

Connections use drivers or ORMs like MongoDB driver, Mongoose, or Sequelize with pooling for performance.
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Q53:

What is the difference between SQL and NoSQL databases?

Junior

Answer

SQL uses tables and schemas; NoSQL uses flexible JSON-like documents or key-value stores.
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Q54:

What is a RESTful API?

Junior

Answer

A RESTful API uses HTTP verbs and structured endpoints to perform operations.
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Q55:

Why is logging important in Node apps?

Junior

Answer

Logging helps track errors, performance, and user actions. Winston and Pino are common tools.
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Q56:

What is the purpose of versioning an API?

Junior

Answer

Versioning prevents breaking old clients when adding new features.
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Q57:

What is the difference between require and import?

Junior

Answer

require is CommonJS; import is ES modules. Both load modules but with different syntax rules.
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Q58:

What is Express error-handling middleware?

Junior

Answer

A special middleware with four parameters used to catch and manage errors in Express apps.
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Q59:

What are static files in Node.js?

Junior

Answer

Static files like images, CSS, or JS are served as-is without processing.
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Q60:

What is the purpose of package-lock.json?

Junior

Answer

package-lock.json stores exact dependency versions for consistent installations.
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Q61:

How does the Node.js event loop differ from traditional multi-threaded servers?

Mid

Answer

Traditional servers create threads per request. Node.js uses a single-threaded event loop and offloads heavy tasks to worker threads, making it efficient for I/O-heavy workloads.
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Q62:

What are microtasks and macrotasks in the Node.js event loop?

Mid

Answer

Microtasks include promise callbacks and queueMicrotask. Macrotasks include timers, I/O callbacks, and setImmediate. Microtasks run before macrotasks within each event loop cycle.
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Q63:

What is backpressure in Node.js streams?

Mid

Answer

Backpressure occurs when a data source produces data faster than the consumer can handle. Streams manage this using internal buffers and methods like pause() and resume().
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Q64:

How do worker threads improve performance in Node.js?

Mid

Answer

Worker threads run CPU-intensive tasks in parallel without blocking the main thread. They are ideal for cryptography, parsing, and other heavy computations.
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Q65:

Why are synchronous functions discouraged in Node.js?

Mid

Answer

Synchronous functions block the event loop, delaying other requests and reducing server responsiveness.
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Q66:

What is middleware order in Express.js and why is it important?

Mid

Answer

Middleware runs in the order defined. Logging, authentication, and parsers must be placed correctly to ensure proper request handling.
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Q67:

What is a reverse proxy and why is Node.js used behind one?

Mid

Answer

Reverse proxies like Nginx handle SSL, caching, and load balancing. Node apps use them for better security and performance.
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Q68:

What causes memory leaks in Node.js?

Mid

Answer

Memory leaks occur due to unused global variables, unremoved event listeners, unclosed timers, or improper caching.
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Q69:

What are child processes in Node.js?

Mid

Answer

Child processes allow running OS-level processes. Useful for executing scripts, shell commands, or parallel computation.
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Q70:

What is the purpose of the crypto module in Node.js?

Mid

Answer

The crypto module provides hashing, encryption, decryption, signing, and random data generation for secure operations.
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Q71:

How does Express handle error propagation?

Mid

Answer

Calling next(error) skips normal middleware and invokes error-handling middleware for consistent error responses.
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Q72:

What is an HTTP agent in Node.js?

Mid

Answer

An HTTP agent manages and reuses TCP connections, improving the performance of outgoing HTTP requests.
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Q73:

What is the difference between setImmediate and setTimeout?

Mid

Answer

setImmediate runs after the poll phase. setTimeout runs after a delay. Their order may depend on event loop timing.
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Q74:

How does Node.js clustering differ from worker threads?

Mid

Answer

Clustering creates multiple Node processes sharing one port. Worker threads share memory inside one process. Clustering boosts request throughput; workers boost compute tasks.
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Q75:

What is ESM support in Node.js?

Mid

Answer

ESM enables import/export syntax, better static analysis, and improved compatibility with modern JavaScript modules.
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Q76:

What is the purpose of the package exports field?

Mid

Answer

The exports field controls which files of a package are accessible, helping secure internal modules and define public APIs.
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Q77:

How does Node.js handle large JSON parsing?

Mid

Answer

Large JSON parsing blocks the event loop. Solutions include streaming parsers, chunk processing, or using worker threads.
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Q78:

What is an ORM in Node.js and why use one?

Mid

Answer

ORMs like Sequelize or TypeORM map database tables to objects, simplifying queries and enforcing consistency.
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Q79:

How does Mongoose handle schema validation?

Mid

Answer

Mongoose validates data using schema rules such as types, required fields, enums, and custom validators.
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Q80:

What is optimistic vs pessimistic locking?

Mid

Answer

Optimistic locking checks data versions and assumes few conflicts. Pessimistic locking blocks rows until transactions complete.
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Q81:

What is middleware composition?

Mid

Answer

Middleware composition chains multiple middleware functions into a reusable sequence for tasks like validation or authorization.
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Q82:

What are environment-specific configurations?

Mid

Answer

Different environments use different settings such as DB URLs or logging levels, managed via env variables or configs.
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Q83:

What is a health-check endpoint?

Mid

Answer

A health-check endpoint responds with a status like OK to help monitoring tools verify app uptime.
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Q84:

What is the difference between access tokens and refresh tokens?

Mid

Answer

Access tokens are short-lived and used for API calls. Refresh tokens generate new access tokens without re-login.
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Q85:

What is input validation and why is it critical?

Mid

Answer

Input validation ensures request data meets expected formats and prevents injection attacks using libraries like Joi or Zod.
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Q86:

What is rate limiting in Node.js?

Mid

Answer

Rate limiting restricts excessive requests per user to prevent abuse, brute force, and server overload.
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Q87:

How do you manage logs across environments?

Mid

Answer

Structured logging formats like JSON are used with tools such as Winston or Pino for centralized log management.
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Q88:

What is a caching layer and why is it important?

Mid

Answer

Caching stores frequently accessed data to reduce database load and improve response speed. Redis is commonly used.
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Q89:

What is graceful shutdown in Node.js?

Mid

Answer

Graceful shutdown stops accepting new requests, finishes in-flight work, and closes resources before exit.
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Q90:

How do you monitor Node.js apps in production?

Mid

Answer

Monitoring tools like PM2, New Relic, Datadog, or Prometheus track CPU, memory, errors, and endpoint performance.
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Q91:

How does Node.js optimize performance under heavy concurrent load?

Senior

Answer

Node optimizes concurrency using the non-blocking event loop, internal thread pool, keep-alive agents, and efficient memory handling. Scaling further requires clustering, load balancers, event-driven design, and stream-based processing.
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Q92:

How do you design a scalable Node.js architecture for millions of requests?

Senior

Answer

Scale horizontally using clustering and multiple instances behind a reverse proxy. Use caching, message queues, sharding, CDN offloading, and stateless microservices to ensure modular and scalable design.
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Q93:

What is event loop starvation and how do you prevent it?

Senior

Answer

Starvation occurs when CPU-heavy tasks block the event loop. Detect via event loop delay, profiling, and async hooks. Prevent using worker threads or offloading computation to services.
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Q94:

How does Node.js handle high-throughput TCP or WebSocket apps?

Senior

Answer

Node maintains persistent connections, processes messages as streams, and uses buffers efficiently. Its event-driven sockets allow tens of thousands of connections with minimal overhead.
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Q95:

How do you design a fault-tolerant Node.js system?

Senior

Answer

Use supervisors like PM2 or Kubernetes, implement circuit breakers, retries, graceful degradation, dead-letter queues, and distributed load balancing for self-healing architectures.
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Q96:

How does garbage collection impact Node.js performance?

Senior

Answer

GC pauses can affect latency. Optimize by reducing object churn, using pooling, limiting memory consumption, and tuning V8 GC flags for performance.
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Q97:

What are advanced techniques for debugging memory leaks?

Senior

Answer

Use heap snapshots, memory flame graphs, async hooks, and allocation tracking. Identify retained objects, growing listeners, open timers, or closures causing leaks.
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Q98:

How does Node.js provide request isolation in a single thread?

Senior

Answer

Node isolates requests via async boundaries and execution contexts. For stricter isolation, use worker threads, VM sandboxes, or containerization.
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Q99:

What is the role of async_hooks in Node internals?

Senior

Answer

async_hooks track async operation lifecycles. Used for logging, request tracing, correlation IDs, and context propagation.
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Q100:

How do you manage distributed transactions in Node.js?

Senior

Answer

Use saga patterns, event-based compensation, idempotent operations, and message queues. Avoid strict ACID across services.
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Q101:

How do you build a high-performance streaming pipeline?

Senior

Answer

Use backpressure-aware pipelines, transform streams, efficient chunking, and the pipeline() API to safely chain streams.
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Q102:

How do you mitigate Node.js supply chain risks?

Senior

Answer

Mitigate risks using npm audit, dependency pinning, lockfile integrity, and security scanners like Snyk and OSSAR.
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Q103:

What is zero-downtime deployment in Node.js?

Senior

Answer

Achieved using blue-green deployments, rolling updates, graceful connection draining, and orchestration tools like Kubernetes.
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Q104:

How does Node.js handle TLS/SSL and its performance cost?

Senior

Answer

TLS operations are CPU-intensive. Node offloads crypto to worker threads. Performance impacted by cipher suites, key sizes, and session reuse.
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Q105:

How do you design a plugin-based Node.js architecture?

Senior

Answer

Use dependency injection, configuration-driven module loading, versioned modules, and isolated service layers for modular design.
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Q106:

What are Unix domain sockets and why use them?

Senior

Answer

Domain sockets provide fast interprocess communication with lower latency than TCP. Often used between Nginx and Node.
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Q107:

What are advanced caching patterns in Node.js?

Senior

Answer

Use multi-layer caching including in-memory, Redis, CDN, and memoization. Apply TTL rules, stale-while-revalidate, and invalidation strategies.
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Q108:

How do you prevent race conditions in Node.js?

Senior

Answer

Use atomic DB operations, distributed locks, mutexes, or job queues. Avoid shared mutable state in the event loop.
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Q109:

What is vertical vs horizontal scaling in Node.js?

Senior

Answer

Vertical scaling increases machine power; horizontal scaling adds more instances. Node typically scales horizontally.
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Q110:

How do you tune a Node.js app for low latency?

Senior

Answer

Avoid blocking operations, reduce GC pauses, use streams, optimize DB queries, enable keep-alive, and minimize middleware overhead.
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Q111:

What are advanced routing patterns in Node frameworks?

Senior

Answer

Patterns include route grouping, prefixing, controller-based routing, lazy routes, and middleware stacking for large applications.
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Q112:

How do you manage large-scale API versioning?

Senior

Answer

Use URI, header, or content negotiation versioning. Maintain separate controllers and implement deprecation workflows.
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Q113:

What is distributed cache stampede and prevention methods?

Senior

Answer

Prevent stampede using locks, request coalescing, stale responses, or probabilistic expirations.
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Q114:

How do you optimize Node.js for high memory workloads?

Senior

Answer

Use streaming, chunking, worker threads, pagination, simpler object structures, and buffers over large objects.
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Q115:

What is the circuit breaker pattern in Node microservices?

Senior

Answer

Circuit breakers block calls to unstable services and provide fallbacks, preventing cascading failures.
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Q116:

How do you run background jobs reliably in Node.js?

Senior

Answer

Use queues like Bull or BeeQueue, or worker threads. Implement retries, DLQs, scheduling, and monitoring.
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Q117:

What are idempotent APIs and why are they needed?

Senior

Answer

Idempotent APIs produce the same result regardless of repeated calls, crucial for retries and reliability.
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Q118:

How do you analyze CPU bottlenecks in Node.js?

Senior

Answer

Use CPU profiles, flame graphs, and V8 inspector to detect heavy loops, JSON parsing, regex usage, or encryption overheads.
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Q119:

How do you implement distributed tracing in Node.js?

Senior

Answer

Use correlation IDs, async_hooks-based context tracking, and tools like OpenTelemetry, Jaeger, or Zipkin.
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Q120:

What is graceful error recovery in Node.js?

Senior

Answer

Use retries, fallback logic, circuit breakers, timeouts, and structured error responses to maintain uptime during failures.
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Q121:

How would you redesign the Node.js event loop for ultra-low latency systems?

Expert

Answer

Minimize GC interruptions, offload CPU-heavy tasks to native modules, reduce promises, use real-time thread scheduling, pinned threads, predictable memory allocation, and remove unnecessary async layers.
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Q122:

How does Node.js track async context at runtime and what are its limitations?

Expert

Answer

Node uses async_hooks to track async boundaries. Limitations include overhead, incomplete coverage for some libraries, and microtask behavior that complicates context propagation.
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Q123:

How do you build lock-free concurrent algorithms in Node.js?

Expert

Answer

Use SharedArrayBuffer and Atomics with CAS operations to avoid locks. Carefully design non-blocking structures to prevent race conditions and ensure progress without mutual exclusion.
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Q124:

How do you detect and repair event loop stalls in real-time systems?

Expert

Answer

Monitor event loop delay, profile CPU usage, examine GC pauses, inspect slow promise chains, and offload heavy tasks to workers. Use flame graphs to isolate the offending code.
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Q125:

What is a Node.js native addon and when is it needed?

Expert

Answer

Native addons are C/C++ modules compiled for Node. They are used for CPU-heavy tasks such as encryption, compression, image processing, or low-level system access.
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Q126:

How do you optimize Node.js for strict memory predictability?

Expert

Answer

Avoid dynamic structures, preallocate buffers, reduce closures, use object pools, minimize large allocations, and tune V8 heap settings to prevent unpredictable GC behavior.
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Q127:

How does V8 handle hidden classes and why can misuse hurt performance?

Expert

Answer

V8 creates hidden classes for optimized object access. Changing object shape dynamically causes deoptimization, harming performance. Keep object structures consistent.
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Q128:

How can you build a custom garbage collection strategy with Node + native code?

Expert

Answer

Store large memory in native space and manually manage it. Native modules expose custom allocators, bypassing V8 GC and enabling predictable memory lifecycles.
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Q129:

What is a tick-based starvation pattern and how to prevent it?

Expert

Answer

Starvation occurs when microtasks continuously queue themselves. Prevent via batching, inserting setImmediate breaks, or rearchitecting promise recursion.
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Q130:

How do you design a fully distributed Node.js system with no single points of failure?

Expert

Answer

Use multi-zone deployment, redundant brokers, replicated DBs, load balancing, leader election, and self-healing mechanisms across all services.
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Q131:

How do you implement a custom scheduler inside a Node.js application?

Expert

Answer

Use worker threads or child processes with priority queues. Employ cooperative multitasking using event loop checkpoints or manual yielding.
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Q132:

How does cluster.loadBalance work internally?

Expert

Answer

The master process distributes incoming connections to workers. Uses round-robin on Linux and OS-level scheduling on Windows.
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Q133:

How do you process millions of messages per second in Node.js?

Expert

Answer

Use zero-copy buffers, binary protocols, Kafka/Redis pipelines, cluster workers, streaming APIs, domain sockets, and horizontal scaling.
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Q134:

Difference between async resource vs async operation in Node internals?

Expert

Answer

Async resources track handles like sockets or timers. Async operations are actions performed by these resources. Distinguishing them aids context tracking.
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Q135:

How do you build a custom transport protocol in Node.js?

Expert

Answer

Use raw TCP/UDP sockets, define packet frames, implement chunking, ACK logic, retries, and error correction. Avoid HTTP overhead in ultra-low latency scenarios.
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Q136:

Difference between cooperative and preemptive scheduling in Node workers?

Expert

Answer

Workers use cooperative scheduling, requiring manual yielding for fairness. Preemptive scheduling would interrupt tasks at system level, not supported by Node.
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Q137:

How do you debug memory leaks in distributed Node.js environments?

Expert

Answer

Capture remote heap snapshots, compare over time, inspect retained objects, trace async refs, and correlate memory growth with workload patterns.
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Q138:

What is the role of libuv and how does it work with V8?

Expert

Answer

libuv manages I/O, timers, and thread pools. V8 executes JS and handles memory. Both coordinate via event loop phases to run async operations.
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Q139:

How do you ensure strong consistency in distributed Node.js systems?

Expert

Answer

Use quorum reads/writes, distributed locks, idempotent updates, ordered logs, and consensus protocols such as Raft.
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Q140:

How do you design multi-region failover for Node.js APIs?

Expert

Answer

Use global load balancers, DNS routing, replicated DBs, stateless JWT sessions, and latency-based region switching with automated failover.
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Q141:

How do you optimize Node.js for massive file ingestion?

Expert

Answer

Use streams, chunk processing, backpressure handling, zero-copy transfers, and minimal memory buffering for GB/TB-scale ingestion.
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Q142:

Explain nested microtask queue behavior during promise chains.

Expert

Answer

Nested promises can monopolize the microtask queue, blocking I/O. Break chains with setImmediate or timers to restore fairness.
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Q143:

How do you implement distributed rate limiting in Node.js?

Expert

Answer

Use Redis or a distributed store for counters. Implement token bucket, sliding window, or leaky bucket algorithms across nodes.
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Q144:

What are Node.js limitations in CPU-bound workloads?

Expert

Answer

Worker threads still have message-passing overhead, share memory constraints, and GC pauses. Compiled languages outperform Node for heavy CPU tasks.
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Q145:

How do you implement the transactional outbox pattern in Node.js?

Expert

Answer

Write outgoing events inside the same DB transaction, then a background worker reads and publishes them reliably to avoid lost messages.
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Q146:

What is TCP head-of-line blocking and how do you fix it?

Expert

Answer

Head-of-line blocking occurs when a lost TCP packet halts subsequent packets. Mitigate using HTTP/2 multiplexing, UDP, or splitting connections.
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Q147:

How do you design CQRS architecture with Node.js?

Expert

Answer

Split read/write models, use event sourcing for writes, maintain async read models, and use message brokers for decoupling services.
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Q148:

How do you isolate workloads in multi-tenant Node.js systems?

Expert

Answer

Use worker pools, sandboxed VM contexts, strict DB row-level separation, per-tenant caching, and request rate caps.
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Q149:

How do you execute canary deployments for Node.js apps?

Expert

Answer

Release new versions to a small traffic subset, monitor metrics, then expand rollout. Rollback instantly if issues arise.
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Q150:

Difference between backpressure and head-pressure in distributed systems?

Expert

Answer

Backpressure is local flow control on streams. Head-pressure is system-wide congestion caused by downstream overload. Mitigate via queues, throttling, and load shedding.
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