Question 1

How does the built-in HTTP server (node:http) work, and what is the lifecycle of IncomingMessage and ServerResponse objects?

Accepted Answer

node:http uses an event-driven server. req represents a Readable stream for request data, and res is a Writable stream for sending response headers and the body.

Question 2

How do Express Middlewares work, and how does Regular Middleware differ from Error-Handling Middleware?

Accepted Answer

Middlewares run in sequence through calls to next(); Error Middleware takes four arguments (err, req, res, next) and runs only when an error is passed to next(err).

Question 3

Why can Fastify outperform traditional frameworks, and how does Schema-Based Compilation work?

Accepted Answer

Fastify precompiles schemas (JSON Schema) with fast-json-stringify and the find-my-way router, avoiding dynamic processing costs and speeding up serialization.

Question 4

How does NestJS apply Dependency Injection and organize Modules?

Accepted Answer

NestJS uses an IoC Container and Decorators (@Injectable, @Module) to inject services and manage their lifecycles automatically through Constructor Injection.

Question 5

Why is input validation with schema libraries such as Zod important in Node.js?

Accepted Answer

It ensures that client data matches expected types and constraints before it reaches business logic, and helps prevent injection attacks and field tampering.

Question 6

What is Content Negotiation, and how do you handle the Accept and Content-Type headers?

Accepted Answer

It lets the client specify a preferred data format (such as JSON or XML) through Accept, while Content-Type declares the format of the data actually being sent.

Question 7

How do you build an efficient WebSocket server with the ws library and implement a Heartbeat (Ping/Pong)?

Accepted Answer

An HTTP connection is upgraded to a bidirectional socket, and periodic Ping messages check that the connection is alive and close dead sockets (Zombie Connections).

Question 8

How do you safely handle multipart/form-data requests and file uploads in Node.js servers?

Accepted Answer

Use a streaming parser (such as busboy or multer) to inspect boundaries and stream file parts while enforcing strict limits on file size and extension.

Question 9

How do you protect a Node.js server from Slowloris attacks and implement request rate limiting (Rate Limiting)?

Accepted Answer

Protect against Slowloris by setting strict header timeouts (headersTimeout), and apply Rate Limiting with a Token Bucket algorithm and a shared Redis store.

Question 10

When should you prefer Server-Sent Events (SSE) over WebSockets, and how do you implement SSE in Node.js?

Accepted Answer

Prefer SSE when data flows in one direction from the server to the client (such as notifications or streaming AI text), and implement it over an HTTP connection with the text/event-stream header.