10 Essential Node.js Interview Questions Every Developer Should Know

This article shares ten essential Node.js interview questions, providing both Chinese and English versions and linking to an open‑source project for further study.

Q1: What is Node.js?

Node.js is a JavaScript runtime built on Chrome's V8 engine, offering an open‑source, cross‑platform server‑side environment where developers can write JavaScript to create applications that run on Windows, Linux, or macOS.

It is not a new language nor a framework; it executes JavaScript similarly to a browser.

Node.js Features

Highly Scalable – Uses a single‑threaded event‑loop model, allowing one thread to handle many concurrent requests without the overhead of spawning multiple OS threads.

Event‑Driven and Asynchronous – All APIs are non‑blocking, so the next request can be processed without waiting for the previous one to finish.

No Buffering – Node.js never buffers data; it processes streams directly.

Q2: How to Install Node.js?

Download the installer from the official website nodejs.org . For version management, use nvm :

Install nvm:

wget -qO- https://raw.githubusercontent.com/creationix/nvm/v0.33.2/install.sh | bash

List remote versions: nvm ls-remote List local versions: nvm ls Install a specific version: nvm install v6.9.5 Set default version: nvm alias default v6.9.5 Verify Installation $ node Then run a simple script:

console.log("hello world!");

Q3: How to Listen on Port 80?

Listening on port 80 requires super‑user privileges on Unix‑like systems, which is discouraged. Instead, use a reverse proxy such as Nginx or listen on a port above 1024.

Q4: What Is an Error‑First Callback?

An error‑first callback receives an error object as its first argument (null if no error) and subsequent arguments contain the data.

fs.readFile(filePath, function(err, data) {
    if (err) {
        console.log(err);
    }
    return data;
});

Q5: How to Create an HTTP Service in Node.js?

const http = require('http');
const server = http.createServer((request, response) => {
    if (request.url === '/hello') {
        response.writeHead(200, {'Content-Type': 'text/plain'});
        response.end('hello world!');
    } else {
        response.end('OK!');
    }
});
server.listen(3000, '127.0.0.1', () => {
    console.log('service is listening at http://127.0.0.1:3000');
});

Q6: What Are Node.js Core Components?

The core consists of the V8 engine, the libuv library, and Node.js APIs.

libuv – A cross‑platform asynchronous I/O library written in C/C++ used by Node.js for file system and network operations.

V8 Engine – Google’s high‑performance JavaScript engine written in C++.

APIs (Node.js Core Libs) – Provide asynchronous (and optionally synchronous) functions such as fs.readFile.

var fs = require('fs');
fs.readFile('/files/help.txt', function(err, buf) {
    // handle data
});

Q7: What Is “Callback Hell” and How to Avoid It?

Callback hell refers to deeply nested callbacks that make code hard to read and maintain. Solutions include modularizing callbacks, using Promises, generators, or the modern async/await syntax (Node.js ≥ v7.5).

Q8: What Is Event‑Driven Programming in Node.js?

Event‑driven programming executes code in response to events (e.g., clicks, loads). In Node.js, asynchronous operations invoke callbacks when events occur.

result = getJSONfromDestination();
binddata(result);

function json_finished(result) {
    binddata(result);
}

getJSONfromDestination(json_finished);

Q9: What Is NPM and When Do You Need It?

NPM is Node.js’s package manager, allowing installation, removal, and version management of modules defined in package.json . It is required when a project depends on external libraries such as Redis, MongoDB, or HTTP request utilities.

{
  "name": "X",
  "dependencies": {
    "A": "^1.0"
  }
}

{
  "name": "Y",
  "dependencies": {
    "A": "^1.5"
  }
}

Q10: What Can Node.js Do? Ten Application Scenarios

Web development – Express + EJS + MongoDB/MySQL

REST APIs – Restify

Instant messaging – Express + Socket.io

Web crawling – Cheerio / request

Blog systems – Hexo

Forums – Nodeclub

Web slideshows – Cleaver

Front‑end build tools – bower.js

OAuth authentication – Passport

Scheduled tasks – Later

Reading Recommendations

Node.js interview questions repository

Node.js technology stack guide

This article is reproduced with permission from the author “May Jun” and originally published on the “Nodejs技术栈” public account.