Node.js Interview Questions & Answers

// CommonJS (e.g., my_module.js)
const myModule = require('./my_module');
const express = require('express'); // npm package

// ES Modules (e.g., main.mjs)
import { myFunction } from './my_module.mjs';
import express from 'express'; // npm package

// module.js
exports.name = 'Alice'; // module.exports now has a 'name' property
exports.sayHello = () => console.log('Hello');

// module.js
exports = { name: 'Bob' }; // This assignment changes `exports` reference, not `module.exports`
module.exports = { name: 'Charlie' }; // This directly assigns to the object returned by require()

const http = require('http');

const server = http.createServer((req, res) => {
  res.writeHead(200, { 'Content-Type': 'text/plain' });
  res.end('Hello, Node.js HTTP Server!');
});

const PORT = 3000;
server.listen(PORT, () => {
  console.log(`Server running on port ${PORT}`);
});

const EventEmitter = require('events');

class MyCustomEmitter extends EventEmitter {}

const myEmitter = new MyCustomEmitter();

myEmitter.on('userLoggedIn', (username) => {
  console.log(`${username} has logged in!`);
});

myEmitter.emit('userLoggedIn', 'Alice'); // Output: Alice has logged in!
myEmitter.emit('userLoggedIn', 'Bob');   // Output: Bob has logged in!

const express = require('express');
const app = express();

// Custom logging middleware
const loggerMiddleware = (req, res, next) => {
  console.log(`[${new Date().toISOString()}] ${req.method} ${req.url}`);
  next(); // Pass control to the next middleware/route handler
};

app.use(loggerMiddleware); // Apply middleware globally

app.get('/', (req, res) => {
  res.send('Hello from Express!');
});

app.listen(3000, () => console.log('Server running on port 3000'));

    fs.readFile('file.txt', 'utf8', (err, data) => { /* handle data */ });
    

    fs.writeFile('new_file.txt', 'Hello Node!', (err) => { /* handle err */ });