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Node Js · Complete Question Bank
Practice the complete collection of Node Js interview questions including theory, coding, MCQs and real interview problems.
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143
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Scroll through every important Node Js question asked in real interviews. Includes MCQs, subjective questions, and coding prompts.
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fs.readFile('file.txt', (err, data) => { if (err) throw err; console.log(data.toString()); });npm install express
const fs = require('fs');
const data = fs.readFileSync('file.txt');// math.js
module.exports.add = (a,b)=>a+b;
// app.js
const math=require('./math');
console.log(math.add(2,3));process.nextTick(()=>console.log('Next Tick'));
setImmediate(()=>console.log('Immediate'));const EventEmitter=require('events');
const emitter=new EventEmitter();
emitter.on('greet',()=>console.log('Hello!'));
emitter.emit('greet');{ "name": "my-app", "dependencies": { "express": "^4.18.0" } }const url=require('url');
const q=url.parse('https://example.com/home?id=10',true);
console.log(q.host, q.query.id);const express=require('express');
const app=express();
app.get('/',(req,res)=>res.send('Hello World'));
app.listen(3000);const fs=require('fs');
fs.createReadStream('input.txt').pipe(fs.createWriteStream('output.txt'));npm install express npm update express npm uninstall express
const http=require('http');
http.createServer((req,res)=>{
res.write('Hello World');
res.end();
}).listen(8080);async function getData(){
const res=await fetch('https://api.com');
const data=await res.json();
console.log(data);
}const { fork, spawn } = require('child_process');
const child = fork('worker.js'); // new Node process
const run = spawn('ls', ['-lh']); // system commandconst buf = Buffer.from('Hello');
console.log(buf.toString());const fs = require('fs');
fs.createReadStream('input.txt').pipe(fs.createWriteStream('output.txt'));const fs = require('fs');
fs.open('example.txt', 'r', (err, fd) => {
if (err) throw err;
console.log('File opened successfully');
});// Callback Hell Example
fs.readFile('a.txt', () => {
fs.readFile('b.txt', () => {
fs.readFile('c.txt', () => {
console.log('done');
});
});
});app.use((req,res,next)=>{
console.log('Request Time:', Date.now());
next();
});const { MongoClient } = require('mongodb');
const uri = 'mongodb://localhost:27017';
const client = new MongoClient(uri);
await client.connect();
console.log('Connected to MongoDB');if(process.env.NODE_ENV==='production'){console.log('Running in production');}setTimeout(()=>console.log('Timeout'),1000);
setImmediate(()=>console.log('Immediate'));
process.nextTick(()=>console.log('Next Tick'));function greet(){return 'Hello';}
function run(fn){console.log(fn());}
run(greet);npm install express npm list --depth=0
const { fork } = require('child_process');
const worker = fork('worker.js');
worker.on('message', msg => console.log('Message:', msg));// math.js
module.exports.add=(a,b)=>a+b;
// app.js
const { add }=require('./math');
console.log(add(2,3));// Sync
const fs=require('fs');
fs.readFileSync('file.txt');
// Async
fs.readFile('file.txt',()=>console.log('Done'));async function loadData(){
try{
const res=await fetch('https://api.com');
const data=await res.json();
console.log(data);
}catch(err){console.error(err);}
}const assert = require('assert');
assert.strictEqual(2 + 2, 4);const connect = require('connect');
const app = connect();
app.use((req,res)=>{res.end('Hello Connect');});
app.listen(3000);const { Worker } = require('worker_threads');
new Worker('./task.js');const cluster=require('cluster');
const http=require('http');
if(cluster.isPrimary){for(let i=0;i<4;i++)cluster.fork();}
else{http.createServer((req,res)=>res.end('Hello')).listen(3000);}console.time('fetch');
await fetch('https://api.com');
console.timeEnd('fetch');const crypto=require('crypto');
const hash=crypto.createHash('sha256').update('secret').digest('hex');
console.log(hash);app.get('/users',(req,res)=>res.send('List'));
app.post('/users',(req,res)=>res.send('Created'));const mongoose=require('mongoose');
mongoose.connect('mongodb://localhost:27017/mydb');const dns=require('dns');
dns.lookup('google.com',(err,address)=>console.log(address));const https=require('https');
const fs=require('fs');
const opts={key:fs.readFileSync('key.pem'),cert:fs.readFileSync('cert.pem')};
https.createServer(opts,(req,res)=>res.end('Secure!')).listen(443);const passport=require('passport');
app.post('/login',passport.authenticate('local'),(req,res)=>res.send('Logged in'));const punycode=require('punycode/');
console.log(punycode.encode('mañana'));node inspect index.js // open chrome://inspect for debugging
fs.createReadStream('large.txt').pipe(fs.createWriteStream('copy.txt'));const fs=require('fs');
fs.stat('file.txt',(err,stats)=>console.log(stats.size));app.use((err,req,res,next)=>{
console.error(err.stack);
res.status(500).send('Something broke!');
});try {
const data = await getData();
} catch (err) {
console.error('Error fetching data', err);
}const winston = require('winston');
const logger = winston.createLogger({ level:'info', transports:[ new winston.transports.Console() ] });
logger.info('Server started');require('dotenv').config();
const dbUrl = process.env.DATABASE_URL;const assert=require('assert');
describe('Array',()=>{
it('should return -1 when value not found',()=>{
assert.equal([1,2,3].indexOf(4),-1);
});
});test('adds 2 + 2',()=>{
expect(2+2).toBe(4);
});pm2 start app.js --name myapp pm2 logs myapp
pm2 start app.js -i max pm2 monit
process.on('SIGINT',()=>{
server.close(()=>{
console.log('Server closed gracefully');
process.exit(0);
});
});const cache=new Map();
function getUser(id){
if(cache.has(id)) return cache.get(id);
const user=db.find(id);
cache.set(id,user);
return user;
}import rateLimit from 'express-rate-limit';
const limiter=rateLimit({windowMs:60000,max:100});
app.use(limiter);fs.createReadStream('video.mp4').pipe(res);import cluster from 'cluster';
import os from 'os';
if(cluster.isPrimary){os.cpus().forEach(()=>cluster.fork());}import multer from 'multer';
const upload=multer({dest:'uploads/'});
app.post('/upload',upload.single('file'),(req,res)=>res.send('Uploaded'));import jwt from 'jsonwebtoken';
const token = jwt.sign({id:1},'secret',{expiresIn:'1h'});
const decoded = jwt.verify(token,'secret');import compression from 'compression'; app.use(compression());
FROM node:18 WORKDIR /app COPY . . RUN npm install CMD ['npm','start']
node > let x = 10; x * 2 20
setTimeout(()=>console.log('After delay'),1000);
setImmediate(()=>console.log('Next phase'));const buf = Buffer.from('Hello');
console.log(buf.toString());const util=require('util');
const wait=util.promisify(setTimeout);
await wait(1000);const dns=require('dns');
dns.lookup('google.com',(err,addr)=>console.log(addr));const redis=require('redis');
const client=redis.createClient();
client.set('user','John');const WebSocket=require('ws');
const wss=new WebSocket.Server({port:8080});
wss.on('connection',ws=>ws.send('Connected!'));const cors=require('cors');
app.use(cors({origin:'*'}));const tls=require('tls');
const server=tls.createServer({key,cert},()=>console.log('TLS Active'));console.log(process.argv.slice(2)); // node app.js arg1 arg2
Correct Answer: V8
Correct Answer: Single-threaded non-blocking
Correct Answer: require()
Correct Answer: Node Package Manager
Correct Answer: fs
Correct Answer: http.createServer()
Correct Answer: They store binary data
Correct Answer: Asynchronous
Correct Answer: They improve performance by handling multiple tasks
Correct Answer: A value that will be resolved later
Correct Answer: child_process
Correct Answer: To enable multi-core scaling
Correct Answer: Duplex
Correct Answer: Request and Response objects
Correct Answer: helmet
Correct Answer: Cross-Origin Resource Sharing
Correct Answer: NODE_ENV
Correct Answer: events
Correct Answer: Read Eval Print Loop
Correct Answer: package.json
Correct Answer: DELETE