Web Development

🚀 Web Development Interview Questions with Answers — Part 5: Node.js 🧠 111. What is Node.js? Node.js is a JavaScript runtime built on Chrome’s V8 engine. It allows JavaScript to run outside the browser. Features: ✅ Fast execution ✅ Event-driven ✅ Non-blocking I/O ✅ Scalable applications Example: console.log("Hello Node.js"); 🧠 112. Why Use Node.js? Advantages: ✅ Fast performance ✅ Single programming language for frontend & backend ✅ Handles multiple requests efficiently ✅ Huge npm ecosystem Best Use Cases: • APIs • Real-time apps • Chat applications • Streaming services 🧠 113. What is npm? npm stands for: 👉 Node Package Manager Used to install libraries/packages. Example: npm install express Uses: • Install packages • Manage dependencies • Run scripts 🧠 114. Difference Between CommonJS and ES Modules CommonJS : Uses require() : Uses module.exports ES Modules : Uses import : Uses export CommonJS: const fs = require("fs"); ES Modules: import fs from "fs"; 🧠 115. What is Express.js? Express.js is a minimal backend framework for Node.js. Features: ✅ Routing ✅ Middleware support ✅ API development Example: const express = require("express"); const app = express(); app.get("/", (req, res) => { res.send("Hello"); }); 🧠 116. What is Middleware? Middleware functions execute between: Request → Response Uses: • Authentication • Logging • Validation Example: app.use((req, res, next) => { console.log("Middleware"); next(); }); 🧠 117. What is REST API? REST API follows REST architecture principles. Common Methods: • GET • POST • PUT • DELETE Example: app.get("/users", (req, res) => { res.json(users); }); 🧠 118. Difference Between PUT and PATCH PUT : Updates entire resource PATCH : Updates partial resource Example: PUT /user/1 PATCH /user/1 🧠 119. What is JWT? JWT stands for: 👉 JSON Web Token Used for authentication. Structure: Header.Payload.Signature Benefits: ✅ Secure authentication ✅ Stateless sessions 🧠 120. What is Authentication vs Authorization? Authentication : Verifies identity Authorization : Verifies permissions Example: • Login → Authentication • Admin access → Authorization 🧠 121. What is CORS? CORS stands for: 👉 Cross-Origin Resource Sharing It controls resource sharing between different domains. Example: app.use(cors()); 🧠 122. What is dotenv? dotenv loads environment variables from .env file. Example: require("dotenv").config(); .env PORT=5000 🧠 123. What is Event Loop? Event loop handles asynchronous operations in Node.js. Process: 1. Executes synchronous code 2. Handles callbacks 3. Processes async tasks Benefits: ✅ Non-blocking execution ✅ Efficient concurrency 🧠 124. What is Non-Blocking I/O? Node.js can process multiple requests without waiting. Benefits: ✅ Faster performance ✅ Better scalability 🧠 125. What is package.json? package.json stores project metadata and dependencies.

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Difference Between Redux and Context API Redux : Advanced state management : Better for large apps Context API** : Simple global state : Better for smaller apps 🧠 97. What are React Hooks? Hooks allow functional components to use: • State • Lifecycle features Common Hooks: • useState • useEffect • useRef • useMemo • useCallback 🧠 98. What is useRef? useRef stores mutable values without re-rendering. Example: const inputRef = useRef(); Uses: • Access DOM elements • Store previous values 🧠 99. What is useMemo? useMemo optimizes expensive calculations. Example: const result = useMemo(() => { return calculate(data); }, [data]); 🧠 100. What is useCallback? useCallback memoizes functions. Example: const memoFn = useCallback(() => { console.log("Hello"); }, []); 🧠 101. What is Lazy Loading in React? Lazy loading loads components only when needed. Example: const Home = React.lazy(() => import("./Home")); Benefits: ✅ Faster loading ✅ Better performance 🧠 102. What is React Router? React Router handles navigation in React applications. Example: } /> 🧠 103. What are Controlled Components? Form elements controlled by React state. Example: setName(e.target.value)} /> 🧠 104. What are Uncontrolled Components? Form elements managed by DOM itself. Example: 🧠 105. What is Lifting State Up? Moving shared state to common parent component. Benefits: ✅ Better state sharing ✅ Improved synchronization 🧠 106. What is Higher Order Component HOC? HOC is a function that takes component and returns enhanced component. Example: const Enhanced = withAuth(Component); 🧠 107. What are Custom Hooks? Custom hooks reuse logic across components. Example: function useFetch() { // logic } 🧠 108. What is Strict Mode? React Strict Mode helps identify potential issues. Example: 🧠 109. What is Server-Side Rendering SSR? SSR renders React components on server before sending to browser. Benefits: ✅ Better SEO ✅ Faster initial load 🧠 110. Difference Between CSR and SSR CSR : Rendered in browser : Slower initial load : SEO less optimized SSR : Rendered on server : Faster initial load : Better SEO Double Tap ❤️ For Part-5

🚀 Web Development Interview Questions with Answers — Part 4: ReactJS 🧠 81. What is React? React is a JavaScript library used to build user interfaces. It was developed by Meta. Features: ✅ Component-based architecture ✅ Virtual DOM ✅ Reusable UI components ✅ Fast rendering Example: function App() { return Hello React ; } 🧠 82. What are Components in React? Components are reusable building blocks of UI. Types: • Functional Components • Class Components Example: function Welcome() { return Welcome ; } 🧠 83. Difference Between Functional and Class Components Functional Component : Simpler syntax : Uses hooks : Preferred nowadays Class Component : More complex : Uses lifecycle methods : Older approach Functional Example: function App() { return Hello ; } 🧠 84. What is JSX? JSX stands for: 👉 JavaScript XML It allows writing HTML inside JavaScript. Example: const element = Hello ; Benefits: ✅ Cleaner syntax ✅ Easier UI development 🧠 85. What are Props? Props are used to pass data between components. Example: function User(props) { return {props.name} ; } Usage: 🧠 86. What is State? State stores dynamic data inside components. Example: const [count, setCount] = useState(0); Uses: • Form handling • Counters • Dynamic UI updates 🧠 87. Difference Between State and Props State : Managed inside component : Mutable Props : Passed from parent : Immutable 🧠 88. What is useState Hook? useState manages state in functional components. Example: import { useState } from "react"; function Counter() { const [count, setCount] = useState(0); return ( setCount(count + 1)}> {count} ); } 🧠 89. What is useEffect Hook? useEffect handles side effects. Example: useEffect(() => { console.log("Component Loaded"); }, []); Uses: • API calls • Timers • Event listeners 🧠 90. What is Virtual DOM? Virtual DOM is a lightweight copy of real DOM. React updates only changed parts instead of entire page. Benefits: ✅ Faster updates ✅ Better performance 🧠 91. What is Reconciliation? Reconciliation is React’s process of comparing: • Old Virtual DOM • New Virtual DOM Then updating only changed elements. 🧠 92. What are Keys in React? Keys uniquely identify list items. Example: items.map(item => ( • {item.name} )); Benefits: ✅ Better rendering ✅ Efficient updates 🧠 93. What is Prop Drilling? Passing props through multiple nested components unnecessarily. Problem: App → Parent → Child → GrandChild Solution: • Context API • Redux 🧠 94. What is Context API? Context API shares data globally without prop drilling. Example: const UserContext = createContext(); Uses: • Theme management • Authentication • Global settings 🧠 95. What is Redux? Redux is a state management library used in React applications. Concepts: • Store • Actions • Reducers Benefits: ✅ Centralized state ✅ Predictable state updates **🧠 96.

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**Difference Between Synchronous and Asynchronous Programming Synchronous** : Executes line by line Blocking  Asynchronous : Executes independently Non-blocking  Example: setTimeout(() => {    console.log("Hello"); }, 2000); 🧠 61. What is Promise in JavaScript? Promise handles asynchronous operations.  States:  • Pending  • Resolved  • Rejected  Example: const promise = new Promise((resolve, reject) => {    resolve("Success"); }); 🧠 62. What are async and await? Used to simplify asynchronous code.  Example: async function getData() {    const response = await fetch(url); } 🧠 63. What is setTimeout? Runs code after specific delay.  Example: setTimeout(() => {    console.log("Hello"); }, 3000); 🧠 64. Difference Between map(), filter(), and reduce() Method : Purpose map() : Transform array filter() : Filter array reduce() : Reduce array to single value  Example: const nums = [1,2,3];  nums.map(n => n * 2); 🧠 65. What is Destructuring? Extract values from arrays or objects.  Example: const person = {    name: "Deepak" };  const { name } = person; 🧠 66. What is Spread Operator? Spread operator expands elements.  Example: const arr1 = [1,2]; const arr2 = [...arr1, 3]; 🧠 67. What is Rest Operator? Collects multiple values into array.  Example: function sum(...nums) {    console.log(nums); } 🧠 68. What is Template Literal? Template literals allow embedded expressions.  Example: let name = "Narayan";  console.log(Hello ${name}); 🧠 69. What is Optional Chaining? Safely accesses nested properties.  Example: user?.address?.city 🧠 70. Explain this Keyword this refers to current object.  Example: const user = {    name: "Radhe",    greet() {       console.log(this.name);    } }; 🧠 71. Difference Between Function Declaration and Function Expression Declaration : Hoisted  Expression : Not fully hoisted  Example: function test() {}  const demo = function() {}; 🧠 72. What is Prototype? Prototype allows inheritance in JavaScript.  Example: function Person() {}  Person.prototype.age = 25; 🧠 73. What is Prototypal Inheritance? Objects inherit properties from other objects.  Example: child.proto = parent; 🧠 74. What is JSON? JSON stands for: 👉 JavaScript Object Notation  Used for data exchange.  Example: {    "name": "Sanyam",    "age": 26 } 🧠 75. Difference Between localStorage and sessionStorage localStorage : Permanent Shared across tabs  sessionStorage : Temporary Limited to tab 🧠 76. What is NaN? NaN means: 👉 Not a Number  Example: console.log("abc" / 2); 🧠 77. What are Truthy and Falsy Values? Falsy Values:  • false  • 0  • ""  • null  • undefined  • NaN  Everything else is truthy. 🧠 78. What is Debounce? Debounce limits repeated function calls.  Used in:  • Search bars  • Resize events  Example: function debounce(fn, delay) {} 🧠 79. What is Throttle? Throttle limits execution rate.  Example: function throttle(fn, limit) {} **🧠 80. What is Currying?** Currying converts function with multiple arguments into nested functions.  Example: function add(a) {    return function(b) {       return a + b;    }; } Double Tap ❤️ For Part-4

🚀 Web Development Interview Questions with Answers — Part 3: JavaScript 🧠 46. What is JavaScript? JavaScript is a programming language used to make web pages interactive. It is used for: • Form validation • Dynamic content • API calls • Animations • Interactive UI Example: console.log("Hello World"); 🧠 47. Difference Between var, let, and const var : Function scoped Can redeclare Can reassign let : Block scoped Cannot redeclare Can reassign const : Block scoped Cannot redeclare Cannot reassign Example: var a = 10; let b = 20; const c = 30; 🧠 48. What are Data Types in JavaScript? Primitive Data Types: • String • Number • Boolean • Null • Undefined • Symbol • BigInt Non-Primitive: • Object • Array • Function Example: let name = "Sanyam"; let age = 26; let isActive = true; 🧠 49. Difference Between null and undefined null : Intentional empty value undefined : Variable declared but not assigned Example: let a = null; let b; console.log(b); 🧠 50. What is Hoisting? Hoisting means JavaScript moves declarations to the top before execution. Example: console.log(a); var a = 10; Output: undefined 🧠 51. Explain Scope in JavaScript Scope determines where variables are accessible. Types: • Global Scope • Function Scope • Block Scope Example: { let age = 26; } age cannot be accessed outside block. 🧠 52. What is Closure? A closure allows a function to access variables from its outer function even after execution. Example: function outer() { let count = 0; return function inner() { count++; console.log(count); }; } const fn = outer(); fn(); 🧠 53. What is Callback Function? A callback is a function passed into another function. Example: function greet(name, callback) { console.log(name); callback(); } greet("Deepak", function() { console.log("Welcome"); }); 🧠 54. What is Arrow Function? Arrow functions provide shorter syntax. Example: const add = (a, b) => a + b; Benefits: ✅ Cleaner syntax ✅ Lexical this 🧠 55. Difference Between == and === == : Checks value only === : Checks value and type Example: 5 == "5" // true 5 === "5" // false 🧠 56. What is Event Bubbling? Event bubbling means events move from child to parent. Example: button.addEventListener("click", () => { console.log("Button clicked"); }); 🧠 57. What is Event Capturing? Event capturing is opposite of bubbling. Event moves: Parent → Child Example: element.addEventListener("click", fn, true); 🧠 58. What is Event Delegation? Using parent element to handle child events. Benefits: ✅ Better performance ✅ Dynamic elements support Example: parent.addEventListener("click", (e) => { console.log(e.target); }); 🧠 59. What is DOM? DOM stands for: 👉 Document Object Model It represents HTML as objects. Example: document.getElementById("title"); **🧠 60.

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🧠 37. What are CSS Transitions?  Transitions create smooth changes between property values.  Example:

button {
   transition: background 0.3s ease;
}

🧠 38. Difference Between Transition and Animation  Transition : Triggered by event  Simple effects  Animation : Can run automatically  Complex effects  Example:

@keyframes move {
   from { left:0; }
   to { left:100px; }
}

🧠 39. What is transform Property?  transform changes element shape or position.  Example:

div {
   transform: rotate(45deg);
}

Common Functions:  - rotate()  - scale()  - translate()  🧠 40. What is overflow Property?  Controls content overflow behavior.  Values:  - visible  - hidden  - scroll  - auto  Example:

div {
   overflow: scroll;
}

🧠 41. Explain CSS Inheritance  Some CSS properties automatically pass from parent to child.  Example:

body {
   color: blue;
}

Child elements inherit text color.  🧠 42. What is !important?  !important gives highest priority to a CSS rule.  Example:

p {
   color: red !important;
}

🧠 43. What are CSS Preprocessors?  Preprocessors extend CSS functionality.  Popular Preprocessors:  - SASS  - SCSS  - LESS  Features:  ✅ Variables  ✅ Nesting  ✅ Functions  🧠 44. Difference Between SCSS and SASS  SCSS : Uses braces  CSS-like syntax  SASS : No braces  Indentation syntax  SCSS Example:

$color: blue;

h1 {
   color: $color;
}

🧠 45. What is Bootstrap?  Bootstrap is a popular CSS framework used for responsive web development.  Features:  ✅ Responsive grid system  ✅ Prebuilt components  ✅ Faster development  Example:

<button class="btn btn-primary">
   Click Me
</button>

Double Tap ❤️ For Part-3

Sure! Here’s the revised content with ** replacing *: --- 🚀 Web Development Interview Questions with Answers — Part 2: CSS 🧠 21. What is CSS? CSS stands for Cascading Style Sheets. It is used to style and design HTML elements. CSS helps to: • Add colors • Set fonts • Create layouts • Add animations • Make websites responsive Example:

h1 {
   color: blue;
   font-size: 40px;
}

🧠 22. Difference Between Inline, Internal, and External CSS Type : Description Inline CSS : Written inside HTML element Internal CSS : Written inside <style> tag External CSS : Written in separate .css file Inline CSS:

<h1 style="color:red;">Hello</h1>

Internal CSS:

<style>
h1 {
   color: blue;
}
</style>

External CSS:

<link rel="stylesheet" href="style.css">

🧠 23. What is Specificity in CSS? Specificity determines which CSS rule is applied when multiple rules target the same element. Priority Order: 1. Inline CSS 2. ID Selector 3. Class Selector 4. Element Selector Example:

#title {
   color: red;
}

.heading {
   color: blue;
}

ID selector has higher priority. 🧠 24. Explain CSS Box Model Every HTML element is treated as a box. The box model contains: • Content • Padding • Border • Margin Structure:

Margin
 └ Border
    └ Padding
       └ Content

Example:

div {
   padding: 20px;
   border: 2px solid black;
   margin: 10px;
}

🧠 25. Difference Between Margin and Padding Margin : Space outside border Creates gap between elements Padding : Space inside border Creates inner spacing Example:

div {
   margin: 20px;
   padding: 20px;
}

🧠 26. What is Flexbox? Flexbox is a one-dimensional layout system used for alignment and spacing. Benefits: ✅ Easy alignment ✅ Responsive layouts ✅ Flexible spacing Example:

.container {
   display: flex;
   justify-content: center;
   align-items: center;
}

🧠 27. What is CSS Grid? CSS Grid is a two-dimensional layout system. It handles: • Rows • Columns Example:

.container {
   display: grid;
   grid-template-columns: 1fr 1fr;
}

🧠 28. Difference Between Relative, Absolute, Fixed, and Sticky Positioning Position : Description relative : Positioned relative to itself absolute : Positioned relative to parent fixed : Fixed on screen sticky : Sticks during scrolling Example:

div {
   position: absolute;
   top: 20px;
}

🧠 29. What is z-index? z-index controls stack order of elements. Higher z-index appears on top. Example:

.box {
   z-index: 10;
}

🧠 30. Difference Between em, rem, %, px, vh, and vw Unit : Meaning px : Fixed pixels % : Relative percentage em : Relative to parent rem : Relative to root vh : Viewport height vw : Viewport width Example:

h1 {
   font-size: 2rem;
}

🧠 31. What are Pseudo-Classes? Pseudo-classes define special states of elements. Examples:

a:hover {
   color: red;
}

Common Pseudo-Classes: • :hover • :focus • :first-child • :last-child 🧠 32. What are Pseudo-Elements? Pseudo-elements style specific parts of elements. Example:

p::first-letter {
   font-size: 40px;
}

Common Pseudo-Elements: • ::before • ::after • ::first-letter 🧠 33. Difference Between visibility:hidden and display:none visibility:hidden : Element hidden but space remains display:none : Element removed completely Example:

.box {
   display: none;
}

🧠 34. What is Media Query? Media queries make websites responsive. Example:

@media (max-width: 768px) {
   body {
      background: lightblue;
   }
}

🧠 35. Explain Responsive Design Responsive design ensures websites work on: • Mobile • Tablet • Desktop Techniques: ✅ Media Queries ✅ Flexible layouts

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Example: document.cookie = "username=Deepak"; 🧠 15. What are Void Elements? Void elements do not require closing tags. Examples: - <br> - <hr> - <img> - <input> 🧠 16. What is the Purpose of alt Attribute? alt provides alternative text for images. Example: <img src="cat.jpg" alt="Cute Cat"> Benefits: ✅ Accessibility ✅ SEO ✅ Backup text if image fails 🧠 17. Explain Audio and Video Tags HTML5 provides multimedia support. Audio Example: <audio controls> <source src="song.mp3"> </audio> Video Example: <video controls width="400"> <source src="movie.mp4"> </video> 🧠 18. What is Accessibility in HTML? Accessibility means making websites usable for everyone. Best Practices: - Semantic HTML - Alt text - Proper headings - Keyboard support 🧠 19. What are ARIA Attributes? ARIA improves accessibility for screen readers. Example: <button aria-label="Search"> Common ARIA Attributes: - aria-label - aria-hidden - aria-expanded 🧠 20. Difference Between <strong> and <b> <strong> : Semantic importance <b> : Only bold styling <strong> : Used for important text <b> : Used for design Example: <strong>Important</strong> <b>Bold Text</b> Double Tap ❤️ For Part-2

🚀 Web Development Interview Questions with Answers — Part 1: HTML 🧠 1. What is HTML? HTML stands for HyperText Markup Language. It is the standard language used to create and structure web pages. HTML is used to: • Create headings • Add paragraphs • Insert images • Create links • Build forms • Structure web content Example:

<!DOCTYPE html>
<html>
<head>
   <title>My Website</title>
</head>
<body>
   <h1>Hello World</h1>
</body>
</html>

🧠 2. Difference Between HTML4 and HTML5 HTML4 : Older version HTML5 : Latest version HTML4 : No semantic tags HTML5 : Semantic tags added HTML4 : No direct multimedia support HTML5 : Supports audio/video HTML4 : Less mobile friendly HTML5 : Mobile optimized HTML5 Features: • <video> • <audio> • <canvas> • Local Storage • Semantic Tags 🧠 3. What are Semantic Tags in HTML5? Semantic tags describe the meaning of content clearly. Common Semantic Tags: • <header> • <nav> • <section> • <article> • <footer> Benefits: ✅ Better SEO ✅ Better readability ✅ Accessibility improvement Example:

<article>
   <h2>Blog Title</h2>
   <p>Content here...</p>
</article>

🧠 4. Difference Between <div> and <span> <div> : Block element <span> : Inline element <div> : Takes full width <span> : Takes required width <div> : Used for sections <span> : Used for small styling Example:

<div>Hello</div>
<span>Hello</span>

🧠 5. What is the Purpose of DOCTYPE? <!DOCTYPE html> tells the browser which HTML version is being used. Example:

<!DOCTYPE html>

Benefits: ✅ Proper rendering ✅ Avoids browser compatibility issues 🧠 6. What are Meta Tags? Meta tags provide information about the webpage. Example:

<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta name="description" content="HTML Tutorial">

Uses: • SEO • Responsive design • Character encoding 🧠 7. Difference Between ID and Class ID : Unique Class : Reusable ID : Uses # in CSS Class : Uses . in CSS Example:

<div id="header"></div>
<div class="card"></div>
<div class="card"></div>

🧠 8. What are Inline and Block Elements? Block Elements Start on new line Take full width Examples: • <div> • <p> • <h1> Inline Elements Do not start on new line Take only required space Examples: • <span> • <a> • <img> 🧠 9. Explain Forms in HTML Forms collect user input. Example:

<form>
   <input type="text" placeholder="Enter Name">
   <input type="email" placeholder="Enter Email">
   <button>Submit</button>
</form>

Common Form Elements: • input • textarea • select • checkbox • radio button 🧠 10. Difference Between GET and POST GET : Data visible in URL POST : Data hidden GET : Less secure POST : More secure GET : Used for fetching POST : Used for sending Example:

<form method="GET"></form>
<form method="POST"></form>

🧠 11. What is localStorage and sessionStorage? Both store data in browser. localStorage : Permanent sessionStorage : Temporary localStorage : Remains after closing browser sessionStorage : Removed after tab closes Example:

localStorage.setItem("name", "Deepak");
sessionStorage.setItem("theme", "dark");

🧠 12. What are Data Attributes? Custom attributes used to store extra information. Example:

<div data-userid="101">User</div>

Access in JavaScript:

element.dataset.userid

🧠 13. What is iframe? iframe embeds another webpage inside a webpage. Example:

<iframe src="https://example.com"></iframe>

Uses: • YouTube videos • Google Maps • External websites 🧠 14. Difference Between Cookies and localStorage Cookies : Small storage localStorage : Large storage Cookies : Sent to server

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🚀 Top 200 Web Development Interview Questions 🧠 1. HTML Interview Questions (1–20) 1. What is HTML? 2. Difference between HTML4 and HTML5 3. What are semantic tags in HTML5? 4. Difference between <div> and <span> 5. What is the purpose of DOCTYPE? 6. What are meta tags? 7. Difference between ID and Class 8. What are inline and block elements? 9. Explain forms in HTML 10. Difference between GET and POST 11. What is localStorage and sessionStorage? 12. What are data attributes? 13. What is iframe? 14. Difference between cookies and localStorage 15. What are void elements? 16. What is the purpose of alt attribute? 17. Explain audio and video tags 18. What is accessibility in HTML? 19. What are ARIA attributes? 20. What is the difference between strong and b tags? 🎨 2. CSS Interview Questions (21–45) 21. What is CSS? 22. Difference between inline, internal, and external CSS 23. What is specificity in CSS? 24. Explain CSS Box Model 25. Difference between margin and padding 26. What is Flexbox? 27. What is CSS Grid? 28. Difference between relative, absolute, fixed, and sticky positioning 29. What is z-index? 30. Difference between em, rem, %, px, vh, and vw 31. What are pseudo-classes? 32. What are pseudo-elements? 33. Difference between visibility:hidden and display:none 34. What is media query? 35. Explain responsive design 36. What is mobile-first design? 37. What are CSS transitions? 38. Difference between transition and animation 39. What is transform property? 40. What is overflow property? 41. Explain CSS inheritance 42. What is !important? 43. What are CSS preprocessors? 44. Difference between SCSS and SASS 45. What is Bootstrap? ⚡ 3. JavaScript Basics (46–80) 46. What is JavaScript? 47. Difference between var, let, and const 48. What are data types in JavaScript? 49. Difference between null and undefined 50. What is hoisting? 51. Explain scope in JavaScript 52. What is closure? 53. What is callback function? 54. What is arrow function? 55. Difference between == and === 56. What is event bubbling? 57. What is event capturing? 58. What is event delegation? 59. What is DOM? 60. Difference between synchronous and asynchronous programming 61. What is promise in JavaScript? 62. What are async and await? 63. What is setTimeout? 64. Difference between map(), filter(), and reduce() 65. What is destructuring? 66. What is spread operator? 67. What is rest operator? 68. What is template literal? 69. What is optional chaining? 70. Explain this keyword 71. Difference between function declaration and expression 72. What is prototype? 73. What is prototypal inheritance? 74. What is JSON? 75. Difference between localStorage and sessionStorage 76. What is NaN? 77. What are truthy and falsy values? 78. What is debounce? 79. What is throttle? 80. What is currying? ⚛️ 4. ReactJS Interview Questions (81–110) 81. What is React? 82. What are components in React? 83. Difference between functional and class components 84. What is JSX? 85. What are props? 86. What is state? 87. Difference between state and props 88. What is useState hook? 89. What is useEffect hook? 90. What is virtual DOM? 91. What is reconciliation? 92. What are keys in React? 93. What is prop drilling? 94. What is Context API? 95. What is Redux? 96. Difference between Redux and Context API 97. What are React hooks? 98. What is useRef? 99. What is useMemo? 100. What is useCallback? 101. What is lazy loading in React? 102. What is React Router? 103. What are controlled components? 104. What are uncontrolled components? 105. What is lifting state up? 106. What is Higher Order Component (HOC)? 107. What are custom hooks? 108. What is Strict Mode? 109. What is server-side rendering? 110. Difference between CSR and SSR

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