Question 1

What is Node.js and how does it work?

Accepted Answer

Node.js is a JavaScript runtime built on Chrome's V8 engine. It uses an event-driven, non-blocking I/O model ideal for scalable network applications.

Question 2

What is the event loop in Node.js?

Accepted Answer

The event loop is a mechanism that handles asynchronous callbacks in Node.js. It enables non-blocking I/O by pushing operations to the background and executing callbacks when completed.

Question 3

What is Express.js and why is it used?

Accepted Answer

Express.js is a lightweight web application framework for Node.js. It simplifies routing, middleware integration, and server logic.

Question 4

What is the difference between `require` and `import` in Node.js?

Accepted Answer

`require` is CommonJS-based and used in older versions. `import` is ES6 syntax supported in modern versions when using type: module or .mjs files.

Question 5

How can you improve performance in a Node.js application?

Accepted Answer

Use clustering, async programming, caching, and avoid blocking operations. Leverage tools like `pm2` and profiling with `clinic.js`.

Question 6

What is npm and how is it used?

Accepted Answer

npm is the Node Package Manager. It manages project dependencies, scripts, and packages. It is used to install, update, and publish modules.

Question 7

What is the purpose of `process.nextTick()`?

Accepted Answer

`process.nextTick()` schedules a callback to be invoked in the same phase of the event loop, before any I/O or timers. It's used to defer execution until the current stack is cleared.

Question 8

Explain the concept of streams in Node.js.

Accepted Answer

Streams are objects for reading/writing data sequentially. Types: Readable, Writable, Duplex, Transform. They handle large data efficiently without loading everything into memory.

Question 9

What is the difference between `fs.readFile()` and `fs.createReadStream()`?

Accepted Answer

`fs.readFile()` reads the entire file into memory before returning. `fs.createReadStream()` reads the file in chunks, suitable for large files.

Question 10

What is the difference between `setImmediate()` and `setTimeout(fn, 0)`?

Accepted Answer

`setImmediate()` executes callbacks after I/O events in the check phase. `setTimeout(fn,0)` executes in the timers phase. Order depends on the phase when the event loop is at.

Node.js Interview Questions & Answers

What is Node.js and how does it work?

What is the event loop in Node.js?

What is Express.js and why is it used?

What is the difference between `require` and `import` in Node.js?

How can you improve performance in a Node.js application?

What is npm and how is it used?

What is the purpose of `process.nextTick()`?

Explain the concept of streams in Node.js.

What is the difference between `fs.readFile()` and `fs.createReadStream()`?

What is the difference between `setImmediate()` and `setTimeout(fn, 0)`?

How do you handle uncaught exceptions in Node.js?

What is callback hell and how can it be avoided?

What is middleware in Express and how is it used?

How do you handle file uploads in Express?

What is the purpose of `express.Router`?

What are the differences between built-in, local, and third-party modules?

What is the purpose of `package.json` and `package-lock.json`?

How do you enable clustering in Node.js?

What security best practices should you follow in Node.js?

How do you debug a Node.js application?

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