Node.js concurrency explained: Event Loop handles async operations

In one of my recent interviews, I was asked: Why do we add type: "module" in package.json? might seem like a simple question but it checks your fundamentals. By default, Node.js uses CommonJS (require statement) but if we want to use modern import and export, we add: "type": "module" This tells Node to treat our project as an ES Module. Without it, it gives a syntax error. #interview #react #node #nodejs #reactjs #job #js #interviewquestion

𝗧𝗼𝗽 𝗘𝘅𝗽𝗿𝗲𝘀𝘀.𝗷𝘀 𝗜𝗻𝘁𝗲𝗿𝘃𝗶𝗲𝘄 𝗤𝘂𝗲𝘀𝘁𝗶𝗼𝗻𝘀 & 𝗔𝗻𝘀𝘄𝗲𝗿𝘀 — 𝗖𝗼𝗺𝗽𝗹𝗲𝘁𝗲 𝗣𝗿𝗲𝗽𝗮𝗿𝗮𝘁𝗶𝗼𝗻 𝗚𝘂𝗶𝗱𝗲 Prepare for backend and full stack interviews with the most important Express.js interview questions. This guide covers core concepts like middleware, routing, request–response cycle, error handling, REST API design, authentication, performance optimization, and real-world implementation scenarios. Perfect for beginners, intermediate developers, and professionals preparing for Node.js or MERN stack interviews. Master Express.js fundamentals and confidently crack your next technical interview. #ExpressJS #NodeJS #BackendDevelopment #MERNStack #WebDevelopment

📘 40 Node.js Interview Questions – The Key Concepts to Master! 💚 Are you preparing for your next backend developer interview? This Node.js Interview Questions guide is your ultimate revision partner! 🚀 🎯 What’s inside? ✅ 40 essential Node.js questions & answers 🧠 Covers core concepts like Event Loop, Modules, Streams, Buffers, and more ⚙️ Deep dive into npm, middleware, authentication, and child processes 📦 Popular topics: Express.js, Promises, Callback Hell, JWT, Multer, and Cluster 🔐 Real-world concepts: CORS, TLS, Session Management, File Uploads, and Database Connections 💡 Whether you're a beginner or an experienced dev, this guide helps you: · Revise smartly 💪 · Understand tricky concepts 🧩 · Crack interviews with confidence 🎤 📌 Save this for later, share with friends, and follow for more tech content! 👨💻 Created with passion by Muhammad Salman Hussain 🔁 Like, Comment & Share to help others ace their interviews! #NodeJS #JavaScript #InterviewPrep #BackendDevelopment #CodingInterview #WebDevelopment #TechGuide #LearnToCode #Programming #DeveloperCommunity

💡 State vs Props vs Hooks in React JS – Repeated Interview Questions | Day 21 Understanding the difference between State and Props is very important for every React developer. 🔵 State ✔ Manages internal component data ✔ Can change (mutable) ✔ Triggers re-render ⚪ Props ✔ Passed from parent component ✔ Read-only (immutable) ✔ Used for communication 🎯 Interview Tips: State manages data, Props pass data. Mastering this concept makes your React fundamentals strong and helps you crack interviews confidently 🚀 Are you comfortable with State & Props? 👨💻 Follow for daily React, and JavaScript 👉 Arun Dubey #ReactJS #FrontendDevelopment #JavaScript #WebDevelopment #Day21

🚨 Most JavaScript developers cannot clearly explain the Event Loop in interviews. They say: “JavaScript is single-threaded.” That’s not the full story. Here’s what actually happens: 1️⃣ Call Stack executes synchronous code 2️⃣ Web APIs (browser / Node) handle async operations 3️⃣ Completed tasks go to Task Queue 4️⃣ Microtasks (Promises) go to Microtask Queue 5️⃣ Event Loop pushes microtasks first when stack is empty Example: console.log("Start"); setTimeout(() => console.log("Timeout"), 0); Promise.resolve().then(() => console.log("Promise")); console.log("End"); Output: Start End Promise Timeout #JavaScript #FrontendDevelopment #TechInterviews #SoftwareEngineering #Coding

🟢 Node.js trick Interview Question process.nextTick() vs setImmediate() — who wins the race? Both promise immediate execution. But Node schedules them very differently. 🧠 process.nextTick() • Runs right after the current operation finishes • Executes before the event loop continues • Higher priority • Can block the event loop if overused It jumps the queue. ⚡ setImmediate() • Runs in the check phase of the event loop • Executes in the next iteration • Lower priority than nextTick It waits for its turn. Example: setImmediate(() => { console.log("setImmediate") }); process.nextTick(() => { console.log("nextTick"); }): Output: nextTick setImmediate Even though setImmediate sounds faster 😄 This question isn’t about syntax. It tests understanding of: • Event loop phases • Task prioritization • Node’s internal scheduling Same language. Different execution model. #NodeJS #BackendDevelopment #EventLoop #JavaScript #TechInterview

I compiled a small JavaScript + React interview questions for quick revision. It includes common frontend interview topics with questions, answers, and short explanations, such as: • Hoisting, Closures, Event Loop • Promises, Microtasks vs Macrotasks • Virtual DOM & Reconciliation • React Hooks and performance concepts • CSR vs SSR and Hydration Sharing it in case it helps someone preparing for frontend interviews. #javascript #reactjs #FrontendDevelopment #InterviewPreparation #SoftwareEngineering

𝗧𝗼𝗽 𝗥𝗲𝗮𝗰𝘁 𝗜𝗻𝘁𝗲𝗿𝘃𝗶𝗲𝘄 𝗤𝘂𝗲𝘀𝘁𝗶𝗼𝗻𝘀 𝗘𝘃𝗲𝗿𝘆 𝗙𝗿𝗼𝗻𝘁𝗲𝗻𝗱 𝗗𝗲𝘃𝗲𝗹𝗼𝗽𝗲𝗿 𝗦𝗵𝗼𝘂𝗹𝗱 𝗞𝗻𝗼𝘄 Preparing for a React interview? This guide covers the most important React interview questions that help you master both fundamentals and advanced concepts. Topics include Virtual DOM, reconciliation, React hooks, component lifecycle, state management, performance optimization, Context API, Redux, custom hooks, server-side rendering (SSR), and React architecture patterns. Whether you're a beginner or an experienced developer preparing for frontend interviews, these questions will help strengthen your understanding of React internals, improve problem-solving skills, and boost confidence during technical interviews. Perfect for developers targeting roles in modern frontend development and product-based companies. #React #ReactJS #FrontendDevelopment #WebDevelopment #JavaScript #ReactDeveloper #FrontendEngineer #CodingInterview #SoftwareEngineering #ReactInterviewQuestions #TechInterview #LearnReact #ReactHooks #WebDev

𝗧𝗼𝗽 𝗝𝗮𝘃𝗮𝗦𝗰𝗿𝗶𝗽𝘁 𝗜𝗻𝘁𝗲𝗿𝘃𝗶𝗲𝘄 𝗤𝘂𝗲𝘀𝘁𝗶𝗼𝗻𝘀 𝗳𝗼𝗿 𝗗𝗲𝘃𝗲𝗹𝗼𝗽𝗲𝗿𝘀 Preparing for JavaScript interviews? This quick guide covers the most asked concepts including: Scope, Hoisting, Closures, this, Promises, Async/Await, Event Loop, Prototypes, ES6+, Debouncing, and more. Perfect for Frontend, Backend, and Full Stack roles. #JavaScript #JSInterview #FrontendDeveloper #WebDevelopment #CodingInterview #SoftwareEngineer #ReactJS #NodeJS #MERNStack

A Hard Truth from JavaScript & Node.js Interviews After attending multiple JavaScript and Node.js interviews, one pattern became impossible to ignore: 👉 Interviewers don’t start with frameworks. 👉 They start with fundamentals. Before React, Nest, or Express… they test: • Closures • The event loop • Async behavior • Control flow And surprisingly, the same questions were repeated across almost every interview, especially for backend and full-stack roles. 🔥 JavaScript & Node.js Questions I Was Asked Repeatedly 🧠 Core JavaScript Fundamentals • What is a closure? (asked almost every time) • Explain the event loop and order of execution • Microtask vs macrotask queue • Hoisting & the temporal dead zone • == vs === • call, apply, bind • Spread vs rest operator • Shallow copy vs deep copy • Debouncing vs throttling • Event bubbling vs capturing • How JavaScript handles asynchronous operations ⚙️ Async JavaScript & Control Flow • Explain Node.js control flow • What is callback hell? • Explain promises • Promise.all vs allSettled vs any vs race • process.nextTick vs setImmediate vs setTimeout vs setInterval • Why process.nextTick runs before promises & timers 🌐 Node.js Internals • Why Node.js is single-threaded • How Node.js handles concurrency • What is libuv? • What is clustering & when to use it • How do you scale a Node.js application? • Streams and types of streams • What is a buffer in Node.js? • Event emitter vs event listener • Explain REPL 🧩 Ecosystem & Architecture • require vs import • package.json vs package-lock.json • Explain middleware and how it works • Explain JWT authentication flow 🎯 The Biggest Takeaway You can: • Memorize frameworks • Build impressive projects But if your fundamentals are weak, interviews expose that immediately. These topics are not basic. They are essential. That’s why I’m going back to the JavaScript & Node.js fundamentals, revising everything from the ground up. #FrontendInterviews #InterviewPreparation #WebPerformance #SoftwareEngineering