What is a Shim in JavaScript? How to answer in an interview

*** List of 20 most asked JavaScript interview questions:*** 1. What are the different data types in JavaScript? 2. What is the difference between var, let, and const? 3. What is the difference between == and ===? 4. What is hoisting in JavaScript? 5. What are closures in JavaScript? 6. What is the difference between null and undefined? 7. What are arrow functions and how are they different from normal functions? 8. What does this keyword refer to in JavaScript? 9. What is the difference between function declaration and function expression? 10. What is a promise in JavaScript? 11. What is event bubbling and event capturing? 12. What is async/await and how does it work? 13. What is the event loop in JavaScript? 14. What is the difference between synchronous and asynchronous JavaScript? 15. What are higher-order functions in JavaScript? 16.What is the difference between deep copy and shallow copy? 17. What is destructuring in JavaScript? 18. What is prototypal inheritance? 19. What is the difference between map() and forEach()? 20. What are JavaScript modules and how do you use them? #FrontendInterview #JavaScript #FrontendDeveloper #CodingInterview #WebDevelopment #ReactJS #JavaScriptTips

🚀 Day 4 of my 4 Days – 4 JavaScript Questions Challenge! Once in a while, you’ll face this classic interview question: 💭 "What is a Prototype in JavaScript?" I remember the first time I was asked this — I completely blanked out 😅 But you don’t have to! Here’s how you can confidently explain it in your next interview 👇 In JavaScript, every function automatically gets a prototype property, which is an empty object by default. This prototype object is used to add properties and methods that can be shared across all instances created by that function (when used as a constructor with new). function Person(name) {  this.name = name; } // Adding a method to prototype Person.prototype.greet = function() {  console.log("Hello, " + this.name); }; const user1 = new Person("Anurag"); const user2 = new Person("Sachin"); user1.greet(); // Hello, Anurag user2.greet(); // Hello, Sachin Both objects share the same method via the prototype — making it memory-efficient and powerful. 💪 #JavaScript #FrontendDevelopment #WebDevelopment #JSChallenge #LearningByCoding #UIDeveloper #TechJourney #CodingCommunity

🚀 Top 25 Advanced JavaScript Interview Questions You Must Master in 2025 1. What is an execution context, and how does the call stack work? 2. Explain lexical scoping and how JavaScript determines variable access. 3. How does the temporal dead zone (TDZ) affect variable usage? 4.What is hoisting, and how does it differ for `var`, `let`, and `const`? 5. Difference between global, function, and block scope? 6.How do closures work internally, and when should you use them? 7.What are shadowed variables, and how can they cause bugs? 8.How does scope chaining help in variable resolution? 9 What are memory contexts, and how do they relate to garbage collection? 10. What causes memory leaks, and how can they be prevented? 11.How does garbage collection work in modern JS engines? 12.What are WeakMap and WeakSet, and how do they help? 13 Explain deep copy vs shallow copy in JavaScript. 14 What is debouncing vs throttling, and when to use each? 15.Difference between call stack and memory heap? 16. What is tail call optimization, and how does it improve performance? 17. How to detect and fix performance bottlenecks? 18.Difference between Set, Map, WeakMap, and WeakSet? 19.How does event delegation improve memory and performance? 20.Why is immutability important in modern JS? 21.What are side effects, and how to handle them effectively? 22.How does strict mode (`'use strict'`) change execution? 23.What is temporal coupling, and how can modular design reduce it? 24. How do try-catch-finally and error handling work with async code? 25.What is prototype chaining, and how does inheritance work? 💡 Pro Tip: Don’t just memorize — understand the “why” behind every concept. That’s what makes you a great JavaScript & React developer. 📍 Follow for more JavaScript & React deep dives every week! #JavaScript #FrontendInterview #WebDevelopment #ReactDeveloper #MERNStack #CodingPrep #JSAdvanced #InterviewPrep #TechLearning #JavaScriptDeveloper

💡 🧠 𝗝𝗮𝘃𝗮𝗦𝗰𝗿𝗶𝗽𝘁 𝗔𝗿𝗿𝗮𝘆.𝗽𝗿𝗼𝘁𝗼𝘁𝘆𝗽𝗲.𝗺𝗮𝗽() — 𝗘𝘅𝗽𝗹𝗮𝗶𝗻𝗲𝗱 + 𝗣𝗼𝗹𝘆𝗳𝗶𝗹𝗹 𝗜𝗺𝗽𝗹𝗲𝗺𝗲𝗻𝘁𝗮𝘁𝗶𝗼𝗻⚙️ Ever wondered how the map() method works behind the scenes? 👇 🔍 𝗪𝗵𝗮𝘁 𝗶𝘀 𝗺𝗮𝗽()? The map() method in JavaScript is used to transform each element of an array and return a new array — without modifying the original one. ⚡ 𝗛𝗼𝘄 𝗶𝘁 𝘄𝗼𝗿𝗸𝘀: 🧩 It takes a callback function as an argument. 🔁 Executes that function on each element of the array. 🎯 Returns a new array with the transformed results. Example 👇 const numbers = [1, 2, 3]; const doubled = numbers.map(num => num * 2); console.log(doubled); // [2, 4, 6] 💬 𝗜𝗻 𝗝𝗮𝘃𝗮𝗦𝗰𝗿𝗶𝗽𝘁 𝗜𝗻𝘁𝗲𝗿𝘃𝗶𝗲𝘄𝘀 🎤 Sometimes, interviewers ask you to implement the polyfill for the map() method to test your understanding of: -> Prototype chaining 🧬 -> Callback execution 🔁 -> Return behavior 🎯 💭 Implementing polyfills helps you truly understand how built-in methods work internally — not just how to use them. If you’re preparing for a JavaScript interview, this is one of the must-practice questions 💼 ✨ 𝗪𝗵𝗮𝘁 𝗮𝗿𝗲 𝘆𝗼𝘂𝗿 𝗳𝗮𝘃𝗼𝗿𝗶𝘁𝗲 𝗽𝗼𝗹𝘆𝗳𝗶𝗹𝗹𝘀? Comment below 👇 #JavaScript #FrontendDevelopment #WebDevelopment #CodingChallenge #JavaScriptInterview #ReactJS #FrontendEngineer #100DaysOfCode #Polyfill

JavaScript interview Questions #day3rd Loops & Conditions Q1: What are the different types of loops in JavaScript? for loop: Traditional loop with initialization, condition, and increment while loop: Executes while condition is true, checks condition before execution do-while loop: Executes at least once, checks condition after execution for...in: Iterates over enumerable properties of objects for...of: Iterates over iterable values (arrays, strings, etc.) Q2: How does for...in differ from for...of? for...in: Iterates over enumerable property keys (including prototype chain), best for objects for...of: Iterates over iterable values (arrays, strings, maps, sets), doesn't work with plain objects Q3: What is the difference between switch and if-else statements? if-else: Better for range comparisons, complex conditions, boolean checks switch: Better for exact value matching, more readable for multiple discrete values, uses strict comparison Q4: Explain break and continue statements break: Completely terminates the loop or switch statement continue: Skips the current iteration and continues with the next iteration of the loop Q5: What is short-circuit evaluation in JavaScript? Using logical operators (&&, ||) for conditional execution: a && b: Returns a if falsy, otherwise returns b a || b: Returns a if truthy, otherwise returns b Commonly used for default values and conditional execution #javascript #js #interview #questions #topquestions #javascriptinterview #100dayschallange #day3rd #3rdday #learningjavascript #learnjs #learnjavascript #howtoprefaireforjavascriptinterview #daythree

Recently came across a set of interview questions that really made me pause and think — the kind that test how deeply you understand JavaScript, TypeScript, and React beyond just syntax 👇 What’s the actual difference between Types and Interfaces in TypeScript — and when should you use each? What does “Hoisting” really mean in JavaScript, and how does it affect your code execution? Can you write polyfills for `call`, `apply`, and `bind` — from scratch, using plain JavaScript? How would you write a function that returns a duplicated array with deeply cloned values, not just copies of references? Can you make a JS program that generates a random alphanumeric string every single time it runs — never repeating the same value? What are Keys in React, and why are they essential for rendering lists efficiently? And finally, can you build something that shows your browser’s height and width in real time, updating automatically as you resize the window? These were actual questions from a frontend interview I had recently — and honestly, they’re great for both self-evaluation and brushing up fundamentals. Try answering a few in the comments or sharing how you would approach them 👇 #JavaScript #TypeScript #ReactJS #FrontendInterview #WebDevelopment #TechCommunity #CodingChallenge #LearnInPublic

🔁 Async JavaScript — 10 Must-Know Interview Questions (2025 Edition) Understanding asynchronous behavior is one of the most critical skills for every JavaScript developer. Here are the most frequently asked Async JS questions that test how well you know the event loop, promises, and async flow 👇 1️⃣ Explain the event loop, callback queue, and microtask queue. 2️⃣ How does JavaScript handle asynchronous behavior in a single-threaded model? 3️⃣ What are Promises, and how do they improve asynchronous code readability? 4️⃣ What is the difference between callback functions and promises? 5️⃣ How do async/await functions simplify asynchronous code? 6️⃣ What are Generators, and how do they differ from async functions? 7️⃣ How do you manage concurrency and parallelism in JavaScript? 8️⃣ Difference between `Promise.all`, `Promise.any`, `Promise.allSettled`, and `Promise.race`? 9️⃣ How do Web Workers help with performance in async operations? 🔟 What are microtasks vs macrotasks, and why do they matter? 📍 Follow for weekly deep dives into JavaScript, React & MERN concepts! #AsyncJavaScript #JavaScript #WebDevelopment #FrontendInterview #Promises #EventLoop #ReactDeveloper #MERNStack #JSAdvanced #CodingPrep

🚀 Day 2 – Level 2 of my 4 Days JavaScript Challenge! 💡 Today's question: Why is the output of this code unexpected? 🤔 const obj = {}; const a = { id: 1 }; const b = { id: 2 }; obj[a] = "A"; obj[b] = "B"; console.log(obj[a]); // ❓ 🧠 Expected Output: "A" 😅 Actual Output: "B" 👉 Reason: When you use objects as keys in a plain JavaScript object {}, they are automatically converted to strings — specifically "[object Object]". So in the above code: obj[a] ➜ obj["[object Object]"] = "A" obj[b] ➜ obj["[object Object]"] = "B" Both keys collide because they share the same string representation, and the last one ("B") overwrites the first one. ✅ Correct Approach – Use Map instead! const map = new Map(); const a = { id: 1 }; const b = { id: 2 }; map.set(a, "A"); map.set(b, "B"); console.log(map.get(a)); // "A" console.log(map.get(b)); // "B" 🧩 Key Takeaway: Use Map when you need object references as keys — it preserves their identity and avoids overwriting issues. 🔥 Coming up tomorrow – Day 3: One of the most confusing yet important JavaScript interview concepts you must master! #JavaScript #FrontendDevelopment #WebDevelopment #CodingChallenge #CleanCode #InterviewPreparation #TechJourney #Objects #Map #JSInterview

💡 𝗨𝗻𝗱𝗲𝗿𝘀𝘁𝗮𝗻𝗱𝗶𝗻𝗴 𝗝𝗮𝘃𝗮𝗦𝗰𝗿𝗶𝗽𝘁 𝗣𝗿𝗼𝘁𝗼𝘁𝘆𝗽𝗲 (𝗜𝗻 𝗮 𝗪𝗮𝘆 𝗧𝗵𝗮𝘁 𝗔𝗰𝘁𝘂𝗮𝗹𝗹𝘆 𝗦𝘁𝗶𝗰𝗸𝘀) One of the most commonly asked concepts in JavaScript interviews is: 👉 “What is the Prototype in JavaScript?” And honestly… Most developers memorize the definition but never really understand it. Here’s the version that finally clicked for me 👇 🧠 1. Everything in JavaScript is linked to something else. Every object in JS has a hidden property called [[Prototype]] (you access it as __proto__) — and this connects the object to another object that acts as a backup storage. If JS can’t find a property on your object, it looks “up” the chain. ⚙️ 2. This is why your arrays can use .map() You didn’t write the map() function. But your array still has access to it because: myArray → Array.prototype → Object.prototype This chain is called prototype chaining, and that’s how JavaScript shares functions efficiently. 🧩 3. Prototype is basically JavaScript’s version of inheritance. Not like Java or C++. No classes behind the scenes (until ES6 syntactic sugar). Just plain objects linking to other objects. 📌 4. Why Interviewers Ask This Because understanding prototype helps them judge your core JS thinking: • Do you know how methods are shared? • Do you understand how classes actually work under the hood? • Do you get how the engine resolves properties? It reveals depth — not memorization. ⭐ 5. The easiest one-line explanation Prototype is the mechanism JavaScript uses for reusing methods and enabling inheritance through object links. Simple. Clean. Interview-ready. 🔥 Follow or connect Rohan Palankar for more JavaScript fundamentals, frontend interview insights, and real-world React learning content. 💬 What’s one JS concept you struggled with until it finally “clicked”?👇 #JavaScript #FrontendDeveloper #ReactJS #WebDevelopment #InterviewPreparation #FrontendRoles #DeveloperCommunity #Prototype #TechInterviews

Deep JavaScript Series  Have you ever seen your function run before it even exists? It's surprising, right?  That’s **Hoisting** in action. JavaScript scans your file first, stores functions and variables in memory, and then runs the code.   `var` appears as undefined, while `let` and `const` remain hidden in the temporal dead zone until they are declared. JavaScript doesn’t time travel; it just behaves like it does.  #JavaScript #WebDev #Frontend #interview #inteviewTips