React Interview Questions Fundamentals & Components

🚀 It was “just” a counter… or was it? In a recent interview, I was asked to build a simple counter with + and - buttons and make sure the value never goes below 0. Sounds basic, right? But while solving it, I realized it was actually testing: ✔ Understanding of React state ✔ Functional updates ✔ Clean logic implementation ✔ Handling edge cases properly Sometimes interview questions aren’t about complexity — they’re about clarity of fundamentals. The biggest lesson for me? Master the basics. That’s where real confidence comes from. Have you ever faced a “simple” question that turned out to test deeper concepts? 👇 #ReactJS #FrontendDevelopment #JavaScript #InterviewExperience #LearningJourney

Day 3 of my Interview Preparation 🚀 Today I revised some important JavaScript concepts: • What is React? • What is JSX? • Props in React • useState Hook (State management) • Event Handling in React • React Functional Components Consistent learning every day to improve my skills in **JavaScript, React.js, and Web Development**. #javascript #reactjs #webdevelopment #frontenddeveloper #learninginpublic #100daysofcode

Day 46/365 – JS Interview Question 🚀 Promise.resolve() .then(() => { console.log(1); }) .then(() => { console.log(2); }); Promise.resolve() .then(() => { console.log(3); }) .then(() => { console.log(4); }); ✅ Output: 1 3 2 4 💡 Why? Promises run in the microtask queue. The first .then() from both promises gets queued first → prints 1 then 3. After each of those finishes, their next .then() callbacks get queued → prints 2 then 4. JavaScript executes microtasks in order of scheduling. That’s why the output is: 👉 1 3 2 4 #javascript #promises #eventloop #jsinterview #js #interview #microtask

🚨 JavaScript Interview Question What will be the output? const obj = { name: "Frontend", regularFunc: function () { console.log(this.name); }, arrowFunc: () => { console.log(this.name); } }; obj.regularFunc(); obj.arrowFunc(); Both functions are inside the same object. But the output is different. This question tests understanding of: • this binding • Arrow functions vs regular functions • Execution context in JavaScript Many developers assume both will print the same value. What do you think the output will be? #JavaScript #FrontendInterview #ReactJS #FrontendDeveloper #JavaScriptConcepts #ProductBasedCompany

🚨 JavaScript Interview Question What will be the output? const obj = { name: "Frontend", regularFunc: function () { console.log(this.name); }, arrowFunc: () => { console.log(this.name); } }; obj.regularFunc(); obj.arrowFunc(); Both functions are inside the same object. But the output is different. This question tests understanding of: • this binding • Arrow functions vs regular functions • Execution context in JavaScript Many developers assume both will print the same value. What do you think the output will be? #JavaScript #FrontendInterview #ReactJS #FrontendDeveloper #JavaScriptConcepts #ProductBasedCompany

Want to stand out in React interviews? Start by mastering the fundamentals. I created a React Fundamentals Cheat Sheet – Part 1 that highlights some of the most important concepts every frontend developer should know: ⚛️ React core concepts 🧩 Elements vs Components 🛠️ Component creation with JSX & props ⚡ Virtual DOM and performance 🔑 Dynamic lists with keys These are concepts that appear again and again in interviews and real-world React projects. If you understand these well, you're already on the right path as a React developer. #ReactJS #Frontend #JavaScript #WebDevelopment #Developers #TechCommunity

Day 45/365 – JS Interview Question 🚀 var x = 1; function test() { console.log(x); var x = 2; } test(); ✅ Output: undefined 💡 Why? Inside the function, var x is hoisted to the top of its scope. So when console.log(x) runs, the local x already exists — but it hasn’t been assigned 2 yet. That’s why it prints undefined, not 1. #javascript #hoisting #jsinterview #frontend #js #interview #frontendprep

📌 𝗝𝗮𝘃𝗮𝗦𝗰𝗿𝗶𝗽𝘁 & 𝗥𝗲𝗮𝗰𝘁 𝗜𝗻𝘁𝗲𝗿𝘃𝗶𝗲𝘄 𝗖𝗵𝗲𝗰𝗸𝗹𝗶𝘀𝘁 — 𝗦𝗮𝘃𝗲 𝗧𝗵𝗶𝘀 𝗙𝗼𝗿 𝗟𝗮𝘁𝗲𝗿 🚀 #Day33 If you're preparing for interviews, focus on: 🧠 Core JS Fundamentals ⚡ Async & Event Loop 🧩 Array/Object Logic 🏗 Advanced Concepts (Prototype, Bind, Debounce) 💻 Coding Without Built-ins ⚛️ React Hooks & Architecture 🚀 React Native New Architecture (Fabric, TurboModules, Hermes) Master fundamentals. Practice logic daily. Understand architecture deeply. 📌 Save this for your next interview round. Follow Arun Dubey for more related content! #JavaScript #FrontendDevelopment #ReactJS #WebDevelopment #Interviewquestions #CodingInterview

🚨 JavaScript Interview Question What will be the output? const obj = { name: "Frontend", greet: function () { console.log(this.name); } }; const greet = obj.greet; greet(); greet.call(obj); greet.bind(obj)(); This question tests understanding of: • this binding • call() • bind() • Function invocation context Many developers expect all three calls to behave the same. But JavaScript handles this differently depending on how the function is invoked. What do you think the output will be? #JavaScript #FrontendInterview #ReactJS #FrontendDeveloper #JavaScriptConcepts #ProductBasedCompany

A few weeks ago, I talked about closures in JavaScript because it’s a concept that is frequently asked in technical interviews. But closures are not just an interview topic. They are used all the time in real applications — including React. A good example is React’s useState hook. In the simplified example in the image, both functions returned from the outer function still have access to the same `state` variable. Even though the outer function has already finished executing, those inner functions "remember" the environment where they were created. That’s exactly what a closure is. This is the core idea React relies on to preserve state between renders: functions that still have access to values created earlier. Of course, React’s real implementation is more complex, but the underlying concept is the same. Understanding these fundamentals makes React hooks feel much less like magic, and shows how many of the frameworks and libraries we use every day are built on top of simple JavaScript concepts. #React #JavaScript #Frontend #WebDevelopment #SoftwareEngineering