React Interview Prep: Scenario-Based Questions for Front-End Developers

React Interview Question: What are Custom Hooks in React? Answer: Custom hooks are JavaScript functions that allow you to reuse stateful logic across multiple components. They follow the naming convention starting with "use". Example: 𝘧𝘶𝘯𝘤𝘵𝘪𝘰𝘯 𝘶𝘴𝘦𝘞𝘪𝘯𝘥𝘰𝘸𝘞𝘪𝘥𝘵𝘩() {  𝘤𝘰𝘯𝘴𝘵 [𝘸𝘪𝘥𝘵𝘩, 𝘴𝘦𝘵𝘞𝘪𝘥𝘵𝘩] = 𝘶𝘴𝘦𝘚𝘵𝘢𝘵𝘦(𝘸𝘪𝘯𝘥𝘰𝘸.𝘪𝘯𝘯𝘦𝘳𝘞𝘪𝘥𝘵𝘩)  𝘶𝘴𝘦𝘌𝘧𝘧𝘦𝘤𝘵(() => {   𝘤𝘰𝘯𝘴𝘵 𝘩𝘢𝘯𝘥𝘭𝘦𝘙𝘦𝘴𝘪𝘻𝘦 = () => 𝘴𝘦𝘵𝘞𝘪𝘥𝘵𝘩(𝘸𝘪𝘯𝘥𝘰𝘸.𝘪𝘯𝘯𝘦𝘳𝘞𝘪𝘥𝘵𝘩)   𝘸𝘪𝘯𝘥𝘰𝘸.𝘢𝘥𝘥𝘌𝘷𝘦𝘯𝘵𝘓𝘪𝘴𝘵𝘦𝘯𝘦𝘳("𝘳𝘦𝘴𝘪𝘻𝘦", 𝘩𝘢𝘯𝘥𝘭𝘦𝘙𝘦𝘴𝘪𝘻𝘦)   𝘳𝘦𝘵𝘶𝘳𝘯 () => 𝘸𝘪𝘯𝘥𝘰𝘸.𝘳𝘦𝘮𝘰𝘷𝘦𝘌𝘷𝘦𝘯𝘵𝘓𝘪𝘴𝘵𝘦𝘯𝘦𝘳("𝘳𝘦𝘴𝘪𝘻𝘦", 𝘩𝘢𝘯𝘥𝘭𝘦𝘙𝘦𝘴𝘪𝘻𝘦)  }, [])  𝘳𝘦𝘵𝘶𝘳𝘯 𝘸𝘪𝘥𝘵𝘩 } Explanation: Custom hooks help: 1. reuse logic 2. reduce duplicate code 3. improve component readability Follow-up Interview Question: Do custom hooks share state between components? Answer: No. Explanation: Each component calling the hook gets its own independent state instance. #reactjs #CustomHooks #FrontendDevelopment #WebDevelopment

⚛️ React Interview Question Why can’t we use async/await directly inside useEffect? At first, it feels natural to write this: useEffect(async () => { const data = await fetchData(); setData(data); }, []); But React will complain. Because useEffect expects either: • nothing • or a cleanup function Example of cleanup: - useEffect(() => { const id = setInterval(() => { console.log("running..."); }, 1000); return () => clearInterval(id); }, []); When you make the effect function async, it returns a Promise, not a cleanup function. And React doesn’t know how to handle that. The Correct Pattern Define an async function inside the effect: useEffect(() => { const fetchData = async () => { const data = await getUsers(); setUsers(data); }; fetchData(); }, []); Small detail. Understanding why it happens is more important than memorizing the fix. #ReactJS #FrontendInterview #JavaScript #WebDevelopment #TechCareers

🚀 Frontend Interview Questions Sharing some interesting JavaScript & React interview questions that are commonly asked in frontend interviews. 1️⃣ Write code for Deep Copy without using built-in methods. 2️⃣ Write a program to generate the Fibonacci Series. 3️⃣ Write code for a Higher Order Component (HOC) in React. 4️⃣ Implement Debouncing in JavaScript. 5️⃣ Write a polyfill for Array.prototype.reduce(). 6️⃣ Explain the JavaScript Event Loop. 7️⃣ What happens internally when we type a URL in the browser and press Enter? 8️⃣ Explain the difference between call, apply, and bind in JavaScript. 9️⃣ Explain Event Bubbling and Event Capturing with examples. 🔟 What are the trade-offs between Redux and Context API? 💡 These are great questions to test JavaScript fundamentals and React knowledge. Curious to hear how you would answer these — feel free to share your thoughts in the comments 👇 #javascript #reactjs #frontenddevelopment #webdevelopment #interviewpreparation #softwareengineering

🚀 Custom Hooks in React – Explained in Simple Words (Interview Ready) Day18 If you're preparing for React interviews, you MUST understand Custom Hooks clearly. Let’s break it down 👇 1️⃣ What is a Custom Hook? A Custom Hook is a reusable function in React that uses built-in hooks like useState or useEffect. 👉 It helps avoid repeating the same logic in multiple components. 2️⃣ Why do we use Custom Hooks? ✅ Reuse logic ✅ Keep components clean ✅ Make code easier to understand ✅ Improve maintainability 3️⃣ Can Custom Hooks share state between components? ⚠️ No. Each component using a custom hook gets its own separate state. If you want shared state → use Context API or Redux. This is a very common interview trick question. 4️⃣ Custom Hook vs Normal Function Normal Function: Cannot use React hooks Custom Hook: Can use React hooks Must start with "use" 5️⃣ When should we create a Custom Hook? When the same logic is used in multiple components. Instead of repeating code → move that logic into a custom hook. 🔥 Real-Life Example (Interview Favorite) import { useState, useEffect } from "react"; function useFetch(url) {  const [data, setData] = useState(null);  useEffect(() => {   fetch(url)    .then(res => res.json())    .then(result => setData(result));  }, [url]);  return data; } This helps reuse API logic across multiple components. 💡 Interview One-Line Answer: "Custom Hooks allow us to extract and reuse stateful logic without changing the component structure." If you're preparing for Senior React roles, mastering Custom Hooks is non-negotiable. 👨💻 Follow for daily React, and JavaScript 👉 Arun Dubey Follow for more React interview content 🚀 #ReactJS #FrontendDeveloper #JavaScript #WebDevelopment #ReactHooks #CodingInterview #SoftwareEngineer

🚀 5 React Interview Questions Every Developer Should Know Preparing for a React interview? Here are some commonly asked questions with simple answers. 1️⃣ What is React? React is a JavaScript library for building user interfaces using reusable components and a virtual DOM for efficient updates. 2️⃣ What is the Virtual DOM? The Virtual DOM is a lightweight copy of the real DOM. React updates the Virtual DOM first and then efficiently updates only the changed parts in the real DOM. 3️⃣ What are React Hooks? Hooks allow functional components to use state and lifecycle features. Example: useState, useEffect, useContext. 4️⃣ What is the difference between State and Props? • Props → Passed from parent to child components (read-only). • State → Managed within the component and can change over time. 5️⃣ What is useEffect used for? useEffect is used to handle side effects like API calls, subscriptions, and updating the DOM after rendering. 💡 Tip: Focus on understanding concepts instead of memorizing answers. #ReactJS #Frontend #WebDevelopment #JavaScript #MERN #ReactInterview #CodingInterview #Developer

𝗧𝗼𝗽 𝟮𝟱 𝗥𝗲𝗮𝗰𝘁 𝗜𝗻𝘁𝗲𝗿𝘃𝗶𝗲𝘄 𝗤𝘂𝗲𝘀𝘁𝗶𝗼𝗻𝘀 𝗮𝗻𝗱 𝗔𝗻𝘀𝘄𝗲𝗿𝘀 | 𝗥𝗲𝗮𝗰𝘁𝗝𝗦 𝗜𝗻𝘁𝗲𝗿𝘃𝗶𝗲𝘄 𝗣𝗿𝗲𝗽𝗮𝗿𝗮𝘁𝗶𝗼𝗻 In this video, we cover the most frequently asked React Interview Questions that are commonly asked in product-based and service-based companies. If you are preparing for Frontend Developer or React Developer interviews, this video will help you understand important React concepts clearly. Topics covered in this video: React Virtual DOM React Hooks (useState, useEffect) Functional vs Class Components React Lifecycle Methods React Performance Optimization Controlled vs Uncontrolled Components Props vs State React Context API React Memo, useMemo, useCallback React Rendering and Reconciliation These questions are very helpful for developers with 1–5 years of experience preparing for React interviews. #ReactJS #ReactInterviewQuestions #FrontendDeveloper #JavaScript #WebDevelopment #ReactDeveloper #CodingInterview #Programming

If someone asked you to implement ReactDOM.render from scratch in a 45-minute interview… would you know where to start? This is a classic challenge used by companies like Meta to separate developers who use frameworks from engineers who truly understand them. Understanding the tree structure At its core, a Virtual DOM is simply a tree of plain JavaScript objects representing the real DOM. Instead of heavy DOM nodes, you work with lightweight objects containing properties like tagName, attrs, and children. Converting this object tree into the real DOM isn’t magic, it’s just structured tree traversal. The implementation strategy To build your own render function, you only need to chain three native operations: 1. Identify the node type -If the virtual node is a string → document.createTextNode -If it’s an object → document.createElement 2. Handle the attributes Loop through the attrs object and apply them using setAttribute. 3. Recursion is the engine Iterate through the children array, call the render function recursively, and append each result using appendChild. That’s it. The “magic” behind libraries like React is really just strong JavaScript fundamentals + data structures. Most candidates memorise hooks and APIs. Few can build the core from first principles. And that’s exactly what interviews test. Have you ever read the source code of your favourite framework? What surprised you the most? For more front end interview breakdowns like this, check out GreatFrontEnd. We focus on the concepts that actually get asked in real interviews. https://lnkd.in/dDNuYcKB #frontendinterviews #javascript #reactjs #webdevelopment #greatfrontend

45-minute interview challenge: “Implement ReactDOM.render from scratch.” Sounds scary at first — until you realize what’s really happening under the hood. At its core, React’s rendering isn’t magic. A Virtual DOM is just a tree of plain JavaScript objects. Each node represents either: A text node Or an element with tagName, attrs, and children Rendering this tree into the real DOM comes down to three simple ideas: ✅ Identify the node type String → document.createTextNode Object → document.createElement ✅ Apply attributes Loop over props and attach them with setAttribute. ✅ Use recursion Traverse children, call render again, and appendChild each result. That’s literally it — structured tree traversal. My takeaway: Frameworks abstract complexity, but interviews like this test whether you understand the fundamentals beneath them. Once you break it down, you realize React rendering is just: 👉 Objects 👉 Recursion 👉 Native DOM APIs As frontend engineers, it’s powerful to know why things work — not just how to use them. Great reminder from GreatFrontEnd Always worth revisiting the basics. 🚀

🚀 7 Advanced React JS Interview Questions Every Developer Should Know React interviews often focus on deeper concepts like performance, architecture, and state management. Understanding these topics helps you build scalable and efficient applications. Here are 7 advanced React questions with brief explanations: 1️⃣ What is the Virtual DOM and how does it improve performance? The Virtual DOM is a lightweight copy of the real DOM. React compares changes in the Virtual DOM and updates only the necessary parts in the real DOM, improving performance. 2️⃣ What is the difference between useMemo and useCallback? • useMemo → Memoizes the result of a function. • useCallback → Memoizes the function itself to prevent unnecessary re-creation. 3️⃣ What are Higher Order Components (HOC)? A Higher Order Component is a function that takes a component and returns a new enhanced component with additional functionality. 4️⃣ What is React Context API? Context API allows data to be shared globally across components without passing props manually through every level. 5️⃣ What is code splitting in React? Code splitting allows loading only the necessary parts of an application using React.lazy() and Suspense, improving performance and load time. 6️⃣ What is reconciliation in React? Reconciliation is the process React uses to compare the previous Virtual DOM with the new one and efficiently update the UI. 7️⃣ What is server-side rendering (SSR) in React? SSR renders React components on the server instead of the browser, improving SEO and initial page load performance. 💡 Mastering these concepts helps developers build high-performance and scalable React applications. #ReactJS #FrontendDevelopment #WebDevelopment #JavaScript #MERN #CodingInterview #Developer #Programming

🚀 **Master These 20 JavaScript Interview Questions** If you're preparing for your next JavaScript interview, these 20 questions cover the fundamentals every developer should know: 1️⃣ What is a closure, and how is it used in real-world scenarios? 2️⃣ How does hoisting work for variables and functions? 3️⃣ Can you explain the event loop and how JavaScript handles asynchronous tasks? 4️⃣ What are Promises, and how do they manage async operations? 5️⃣ How does `async/await` simplify working with Promises? 6️⃣ Why don’t arrow functions have their own `this`? 7️⃣ What is destructuring and when should you use it? 8️⃣ What’s the difference between the spread operator and rest parameters? 9️⃣ How does prototype-based inheritance work in JavaScript? 🔟 What determines the value of `this` in different execution contexts? 1️⃣1️⃣ How do ES6 classes work, and how do they differ from constructor functions? 1️⃣2️⃣ Why are JavaScript modules important in modern applications? 1️⃣3️⃣ When should you use `map()` and `filter()`? 1️⃣4️⃣ How does `reduce()` accumulate values into a single output? 1️⃣5️⃣ What’s the difference between `setTimeout` and `setInterval`? 1️⃣6️⃣ How do template literals improve string manipulation? 1️⃣7️⃣ What is type coercion, and why can it be unpredictable? 1️⃣8️⃣ What are truthy and falsy values in JavaScript? 1️⃣9️⃣ When should you use debouncing vs throttling? 2️⃣0️⃣ What is currying, and how does it enhance function reusability? If you're preparing for interviews or sharpening your fundamentals, these questions are a great place to start. #JavaScript #Frontend #WebDevelopment #Interviews #Coding #TechCareers