React Custom Hooks Explained

⚛️ A React interview experience that reminded me why fundamentals matter. During a recent discussion with a friend who appeared for a React Developer interview, something interesting came up. He expected the interview to focus mostly on frameworks, libraries, and tools used in modern frontend development. But the interviewer took a different direction. Instead of asking only about tools, the discussion quickly moved toward React fundamentals and core JavaScript concepts. Questions started coming from different areas: Component lifecycle. Hooks. State management. Performance optimization. That conversation made one thing clear: In React interviews, companies often care more about your understanding of fundamentals than the number of libraries you know. Here are some important React interview questions that often come up: 1️⃣ What is the difference between functional components and class components? 2️⃣ What are React Hooks, and why were they introduced? 3️⃣ What is the purpose of useEffect in React? 4️⃣ What is the difference between useMemo and useCallback? 5️⃣ What are controlled and uncontrolled components? 6️⃣ What is the Virtual DOM, and how does it improve performance? 7️⃣ What is state lifting in React? 8️⃣ How do you optimize performance in a React application? 9️⃣ What is the difference between Context API and Redux? 🔟 How does React reconciliation work? Preparing frameworks is important. But interviews often go deeper than that. Sometimes the most important thing you can prepare is a strong understanding of React fundamentals. 💬 Developers: What was the most interesting React interview question you were asked? #ReactJS #frontend #webdevelopment #interviewexperience #softwareengineering #developers #learning

🚀 3 Tricky React Interview Questions Asked in Top Companies These are NOT your typical “what is useState?” questions. These are the ones that actually test your real understanding of React 👇 ⸻ 1️⃣ Why does a component re-render even with React.memo? You wrapped a child with React.memo. Props look the same… but it still re-renders. 👉 Reason: React.memo does shallow comparison 👉 Objects, arrays, and functions create new references every render 💡 Fix: Use useMemo / useCallback to stabilize references ⸻ 2️⃣ Why is useEffect running twice in development? You used an empty dependency array, still it runs twice 🤯 👉 This is NOT a bug 👉 It’s React Strict Mode (React 18+) 💡 React intentionally mounts → unmounts → mounts again to detect side effects & bugs early ✅ Happens only in development, not in production ⸻ 3️⃣ Why is state not updating inside async functions? You update state, but inside setTimeout or async code it still shows the old value 😵 👉 Reason: Stale closures (JavaScript behavior) 💡 Fix: ✔️ Use functional updates → setState(prev => prev + 1) ✔️ Or useRef for latest value ⸻ 🎯 Interview Tip: Use these keywords to stand out: ✔️ Shallow comparison ✔️ Reference equality ✔️ Strict Mode behavior ✔️ Stale closures #ReactJS #FrontendDeveloper #WebDevelopment #JavaScript #InterviewPrep #ReactInterview #Coding #interview #prepration #Developer

Cracking frontend interviews is not about knowing React. It’s about mastering 3 things: 𝗝𝗮𝘃𝗮𝗦𝗰𝗿𝗶𝗽𝘁 + 𝗙𝗿𝗼𝗻𝘁𝗲𝗻𝗱 𝗙𝘂𝗻𝗱𝗮𝗺𝗲𝗻𝘁𝗮𝗹𝘀 + 𝗦𝘆𝘀𝘁𝗲𝗺 𝗧𝗵𝗶𝗻𝗸𝗶𝗻𝗴 Here are the most asked frontend interview problems 👇 𝗝𝗮𝘃𝗮𝗦𝗰𝗿𝗶𝗽𝘁 (𝗠𝘂𝘀𝘁 𝗵𝗮𝘃𝗲): 1. Implement debounce and throttle from scratch 2. Explain event loop with real examples 3. Write polyfills (map, reduce, bind) 4. Closures and practical use cases 5. Promise handling (all, race, async/await) 𝗙𝗿𝗼𝗻𝘁𝗲𝗻𝗱 (𝗥𝗲𝗮𝗹 𝘄𝗼𝗿𝗸 𝘀𝗸𝗶𝗹𝗹𝘀): 1. Build a form with proper validation 2. Create reusable components (modal, toast) 3. Implement infinite scroll 4. Optimize re-renders in React 5. Make UI responsive and accessible 𝗙𝗿𝗼𝗻𝘁𝗲𝗻𝗱 𝗦𝘆𝘀𝘁𝗲𝗺 𝗗𝗲𝘀𝗶𝗴𝗻 (𝗗𝗶𝗳𝗳𝗲𝗿𝗲𝗻𝘁𝗶𝗮𝘁𝗼𝗿): 1. Design autocomplete search 2. Build a scalable dashboard 3. Handle API caching on client 4. Design real-time features 💡 Most candidates fail not because they can’t code but because they can’t connect these concepts together. If you’re preparing for frontend interviews, focus less on tools and more on how things work under the hood. Which round do you find the hardest — JavaScript, frontend, or system design? 👇 #Frontend #JavaScript #React #CodingInterview #SoftwareEngineering #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

🚀 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

🚀 Frontend Interview Experience (4.5 Years Exp) Recently appeared for a Frontend Developer interview, and these were some interesting questions asked during the discussion. I thought I’d share them with the community, which can help others who are preparing. 👇 1️⃣ JavaScript Method Chaining - Implement an object so it works like this: calculate.add(2).mul(4).subs(1).value 2️⃣ CSS Concept - What is the difference between rem and em units? 3️⃣ React Question - Create a custom hook to build a simple counter app. 4️⃣ React Component Communication - Create two components where: The parent passes a function as a prop, and the child calls that function Two buttons: Button 1 → Increase the child state value Button 2 → Show the current child state value when parent component's button clicked These questions tested JavaScript fundamentals, CSS understanding, and React component communication patterns. 💡 If you’re preparing for Frontend / React interviews, try implementing these without looking up the solution first. Happy learning! 🚀 #javascript #reactjs #frontenddeveloper #webdevelopment #interviewexperience #codinginterview #reacthooks #InterviewPrep

🚀 React Interview Series | Day 4: Why do we actually need "key"? I’ve seen many developers use key in React… but very few can explain why it actually matters. Let’s break it down 👇 💡 The Problem: When rendering a list: {items.map((item) => ( <li>{item.name}</li> ))} React throws a warning: ⚠️ Each child in a list should have a unique "key" prop Most people fix it… without understanding it. 🧠 The Real Reason: React uses a process called Reconciliation to update the UI efficiently. 👉 Without key, React compares elements blindly 👉 With key, React knows exactly: Which item changed Which item was added Which item was removed This makes updates faster and predictable ✅ Correct Usage: {items.map((item) => ( <li key={item.id}>{item.name}</li> ))} 🚫 Common Mistake: Using index as key: key={index} ❌ This breaks when: List is reordered Items are added/removed dynamically 🎯 Interview One-liner Answer: “Keys help React identify which items changed, added, or removed for efficient re-rendering.” Youtube Explanation: https://lnkd.in/g4iBu9iM 💬 Have you ever faced bugs because of wrong keys? Let’s discuss in comments 👇 #React #JavaScript #FrontendDevelopment #WebDevelopment #CodingInterview #ReactJS #Developers

𝐑𝐞𝐚𝐜𝐭 𝐮𝐬𝐞𝐄𝐟𝐟𝐞𝐜𝐭 𝐈𝐧𝐟𝐢𝐧𝐢𝐭𝐞 𝐋𝐨𝐨𝐩 𝐈𝐧𝐭𝐞𝐫𝐯𝐢𝐞𝐰 𝐐𝐮𝐞𝐬𝐭𝐢𝐨𝐧 🚨 Many React developers face this problem… but can’t explain why it happens in interview. Question: Why does useEffect cause infinite loop sometimes? Example ❌ const [count, setCount] = useState(0); useEffect(() => { setCount(count + 1); }, [count]); What happens here? ➡ count changes ➡ useEffect runs ➡ setCount updates state ➡ state change triggers useEffect again ➡ loop continues forever This creates an infinite re-render loop. Correct way ✅ useEffect(() => { setCount(prev => prev + 1); }, []); Why this works? Because empty dependency array runs useEffect only once. Tip for React Interviews: Always check dependency array carefully. Most infinite loop bugs come from wrong dependencies. More React interview questions coming 🚀 #ReactJS #useEffect #FrontendDeveloper #JavaScript #WebDevelopment #CodingInterview #ReactInterview #NextJS #SoftwareDeveloper

🚨 Yesterday’s React interview reminded me why fundamentals still matter. A lot of developers think interviews are all about React projects or frameworks. But most of the questions I was asked were actually about JavaScript fundamentals. Here’s how the interview went. The interviewer started simple: “Can you explain ES6 features? Mention any two.” Then he moved deeper into array methods. • What are common array methods in JavaScript? • What is the difference between map() and filter()? • What is the syntax of Array.filter()? Next came something many developers struggle with: “Can you explain Prototype in JavaScript?” Followed by: “What is a Polyfill in JavaScript?” Then suddenly the question turned into a coding challenge. “Can you write a method where map() behaves like filter() using prototype?” That’s when you realize interviews are not about memorizing definitions — they test how well you understand JavaScript internally. Then came a small output-based question: for (let i = 0; i < 4; i++) { console.log(i); i = 4; } console.log(i); And the interviewer asked: “What will be the output and why?” After JavaScript, we moved to React concepts. Questions included: • What React hooks do you commonly use? • Have you used useDeferredValue? • What is the difference between Class Components and Functional Components? • What is the Virtual DOM? What does the diffing algorithm compare? • Explain the Redux lifecycle. Finally, a practical React coding task: “Fetch products from a dummy JSON API using useEffect, display them, and implement a search functionality using an input field.” (find my github repo for the code reference: https://lnkd.in/d_6FJiCH) 💡 My takeaway from this interview: Frameworks change. Libraries evolve. But JavaScript fundamentals remain the backbone of frontend interviews. If your basics are strong, React questions become much easier. For anyone preparing for Frontend / React interviews, focus on: ✔ JavaScript fundamentals ✔ Array methods & prototypes ✔ Output-based questions ✔ React rendering concepts ✔ Practical coding tasks These are still the areas most interviewers explore. Curious to know from other developers 👇 What was the most unexpected question you faced in a frontend interview? #FrontendDeveloper #ReactJS #JavaScript #InterviewExperience #WebDevelopment

🚀 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