{"id":1444,"date":"2025-08-06T06:54:56","date_gmt":"2025-08-06T06:54:56","guid":{"rendered":"https:\/\/www.softwaretraininginchennai.com\/blog\/?p=1444"},"modified":"2025-08-07T12:21:51","modified_gmt":"2025-08-07T12:21:51","slug":"react-js-interview-question","status":"publish","type":"post","link":"https:\/\/www.softwaretraininginchennai.com\/blog\/react-js-interview-question\/","title":{"rendered":"React.js Interview Question"},"content":{"rendered":"<h3><span style=\"color: #333399;\"><strong>What is React.js?<\/strong><\/span><\/h3>\n<ul>\n<li>React is a JavaScript library for building user interfaces, particularly single-page applications.\u00a0It allows developers to create reusable UI components, manage state, and efficiently update the DOM.<\/li>\n<\/ul>\n<h3><span style=\"color: #333399;\"><strong>What are Components in React?<\/strong><\/span><\/h3>\n<ul>\n<li>Components are\u00a0independent and reusable bits of code. They serve the same purpose as JavaScript functions, but work in isolation and return HTML. Components come in two types<strong>,<\/strong><\/li>\n<\/ul>\n<p><span style=\"color: #993300;\">\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0Functional Components (with Hooks)<\/span><\/p>\n<p><span style=\"color: #993300;\">\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 Class Components (with life cycle methods)<\/span><\/p>\n<h3><span style=\"color: #333399;\"><strong>What is JSX?<\/strong><\/span><\/h3>\n<ul>\n<li>JSX combines\u00a0HTML\u00a0and\u00a0JavaScript\u00a0in a single syntax, allowing you to create\u00a0UI components\u00a0in React. It simplifies rendering dynamic content by embedding\u00a0JavaScript\u00a0expressions inside\u00a0HTML-like tags.<\/li>\n<\/ul>\n<table style=\"height: 79px;\" width=\"622\">\n<tbody>\n<tr>\n<td width=\"368\">\n<p style=\"text-align: center;\"><span style=\"color: #993300;\"><strong><em>Const element = &lt;h1&gt;Hello, world! &lt;\/h1&gt;;<\/em><\/strong><\/span><\/p>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<h3><span style=\"color: #333399;\"><strong>What is the Virtual DOM?<\/strong><\/span><\/h3>\n<ul>\n<li>The virtual DOM is a lightweight copy of the real DOM. React uses it to detect changes and update only the parts that changed, improving performance.<\/li>\n<\/ul>\n<h3><span style=\"color: #333399;\"><strong>What is the Difference Between props and state?<\/strong><\/span><\/h3>\n<p><strong>\u00a0\u00a0 <span style=\"color: #993300;\">props<\/span><\/strong><\/p>\n<ul>\n<li>The Data is passed from one component to another.<\/li>\n<li>It is Immutable (cannot be modified).<\/li>\n<li>Props can be used with state and functional components<strong>.<\/strong><\/li>\n<li>Props are read-only<\/li>\n<\/ul>\n<p><span style=\"color: #993300;\"><strong>\u00a0 state<\/strong><\/span><\/p>\n<ul>\n<li>The Data is passed within the component only.<\/li>\n<li>It is Mutable (can be modified).<\/li>\n<li>The state can be used only with the state components\/class component (Before 16.0).<\/li>\n<li>The state is both read and write<\/li>\n<\/ul>\n<h3><span style=\"color: #333399;\"><strong>What are React Hooks?<\/strong><\/span><\/h3>\n<ul>\n<li>Hooks are functions that let you use state and lifecycle methods in functional components.<br \/>\nCommon hooks:<\/li>\n<li><span style=\"color: #993300;\">useState(),<\/span><span style=\"color: #993300;\">useEffect(),<\/span><span style=\"color: #993300;\">useContext(),<\/span><span style=\"color: #993300;\">useRef(),useMemo().<\/span><\/li>\n<\/ul>\n<h3><span style=\"color: #333399;\"><strong>What is the Difference Between Controlled and Uncontrolled Components?<\/strong><\/span><\/h3>\n<ul>\n<li><span style=\"color: #993300;\"><strong>Controlled components<\/strong><\/span>: Form data is handled by React via<strong> useState().<\/strong><\/li>\n<li><span style=\"color: #993300;\"><strong>Uncontrolled components<\/strong><\/span>: Form data is handled by the DOM, accessed using <strong>useRef().<\/strong><\/li>\n<\/ul>\n<h3><span style=\"color: #333399;\"><strong>What is Functional Component?<\/strong><\/span><\/h3>\n<ul>\n<li>A <strong><em>functional component<\/em><\/strong> is a React component defined as a function that accepts <strong><em>props<\/em><\/strong> as an argument and returns JSX.<\/li>\n<\/ul>\n<p><strong>\u00a0<\/strong><\/p>\n<p style=\"text-align: left;\"><em>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<span style=\"color: #993300;\">\u00a0 function Welcome(props) {<\/span><\/em><\/p>\n<p style=\"text-align: left;\"><span style=\"color: #993300;\"><em>\u00a0 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0return &lt;h1&gt;Hello, props.name}&lt;\/h1&gt;;<\/em><\/span><\/p>\n<p style=\"text-align: left;\"><span style=\"color: #993300;\"><em>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 }<\/em><\/span><\/p>\n<h3 style=\"text-align: left;\"><span style=\"color: #333399;\"><strong>What is Class Component?<\/strong><\/span><\/h3>\n<ul>\n<li>Class components are basically\u00a0JavaScript Object Oriented classes with functions you can use to render React components. The advantage of using classes in React is that they contain lifecycle methods that identify when state changes and update the global state or the component state using the keyword this.<\/li>\n<\/ul>\n<p>&nbsp;<\/p>\n<p style=\"text-align: left;\"><em>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <span style=\"color: #993300;\">import React from &#8220;react&#8221;;<\/span><\/em><\/p>\n<p style=\"text-align: left;\"><span style=\"color: #993300;\"><em>\u00a0<\/em><\/span><\/p>\n<p style=\"text-align: left;\"><span style=\"color: #993300;\"><em>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \u00a0class Welcome extends React. Component {<\/em><\/span><\/p>\n<p style=\"text-align: left;\"><span style=\"color: #993300;\"><em>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0render() {<\/em><\/span><\/p>\n<p style=\"text-align: left;\"><span style=\"color: #993300;\"><em>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0return &lt;h1&gt;Hello, {this.props.name}&lt;\/h1&gt;;<\/em><\/span><\/p>\n<p style=\"text-align: left;\"><span style=\"color: #993300;\"><em>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0}<\/em><\/span><\/p>\n<p style=\"text-align: left;\"><span style=\"color: #993300;\"><em>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0}<\/em><\/span><\/p>\n<h3><span style=\"color: #993300;\"><em>\u00a0<\/em><\/span><span style=\"color: #333399;\"><strong>What is the Purpose of keys in React lists?<\/strong><\/span><\/h3>\n<ul>\n<li><em>Keys help React identify which items have changed, are added, or are removed. They <strong>improve performance<\/strong> during list rendering.<\/em><\/li>\n<\/ul>\n<p style=\"text-align: center;\"><em><span style=\"color: #993300;\">{items. Map(item =&gt; &lt;li key={item.id}&gt;{item.name}&lt;\/li&gt;)}<\/span><\/em><\/p>\n<h3><span style=\"color: #333399;\"><strong>What is Redux and why is it used with React?<\/strong><\/span><\/h3>\n<ul>\n<li>Redux is a state management library that stores the application&#8217;s state in a single global store, making state predictable and easier to manage across components.<\/li>\n<\/ul>\n<h3><span style=\"color: #333399;\"><strong>What is React Context API?<\/strong><\/span><\/h3>\n<ul>\n<li>Context API provides a way to <strong>pass data through the component tree<\/strong> without having to pass props manually at every level (useful for themes, auth, etc.).<\/li>\n<\/ul>\n<h3><span style=\"color: #333399;\"><strong>What is memoization in React?<\/strong><\/span><\/h3>\n<ul>\n<li>React provides React.memo() and useMemo() to optimize performance by preventing unnecessary re-renders.<\/li>\n<\/ul>\n<h3><span style=\"color: #333399;\"><strong>What are higher-order components (HOC)?<\/strong><\/span><\/h3>\n<ul>\n<li>A Higher-Order Component is a function that takes a component and returns a new component. It\u2019s used for reusing component logic.<\/li>\n<\/ul>\n<table style=\"height: 62px;\" width=\"756\">\n<tbody>\n<tr>\n<td width=\"425\"><span style=\"color: #993300;\"><strong>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 const EnhancedComponent = withAuth(Component);<\/strong><\/span><\/p>\n<p style=\"text-align: center;\">\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<h3><span style=\"color: #333399;\"><strong>Difference between useEffect and useLayoutEffect?<\/strong><\/span><\/h3>\n<ul>\n<li>useEffect: Runs after paint (asynchronously).<\/li>\n<li>useLayoutEffect: Runs before paint (synchronously), useful for layout-related changes.<\/li>\n<\/ul>\n<h3><span style=\"color: #333399;\"><strong>What are the components of Redux?<\/strong><\/span><\/h3>\n<p><img decoding=\"async\" class=\"wp-image-1448 aligncenter\" src=\"https:\/\/www.softwaretraininginchennai.com\/blog\/wp-content\/uploads\/2025\/08\/Picture6-300x103.png\" alt=\"\" width=\"352\" height=\"121\" srcset=\"https:\/\/www.softwaretraininginchennai.com\/blog\/wp-content\/uploads\/2025\/08\/Picture6-300x103.png 300w, https:\/\/www.softwaretraininginchennai.com\/blog\/wp-content\/uploads\/2025\/08\/Picture6.png 483w\" sizes=\"(max-width: 352px) 100vw, 352px\" \/><\/p>\n<ul>\n<li>Redux has three main components: the store (which holds the application state), actions (which describe what to do), and reducers (which define how the state changes in response to actions)<\/li>\n<\/ul>\n<h3><span style=\"color: #333399;\"><strong>What is React Router?<\/strong><\/span><\/h3>\n<ul>\n<li><span style=\"color: #333300;\"><a style=\"color: #333300;\" href=\"https:\/\/www.simplilearn.com\/tutorials\/reactjs-tutorial\/routing-in-reactjs\">React Router<\/a>\u00a0<\/span>library adds navigation and routing to single page React applications. It lets you define routes and navigate between different components without reloading the page.<\/li>\n<\/ul>\n<h3><span style=\"color: #333399;\"><strong>Why do we need to React Router?<\/strong><\/span><\/h3>\n<ul>\n<li>React Router allows seamless navigation in a single-page application (SPA) by managing URL changes without refreshing the page, improving user experience and enabling multi-view applications.<\/li>\n<\/ul>\n<h3><span style=\"color: #333399;\"><strong>How do you implement React routing?<\/strong><\/span><\/h3>\n<p><img fetchpriority=\"high\" decoding=\"async\" class=\"wp-image-1446 aligncenter\" src=\"https:\/\/www.softwaretraininginchennai.com\/blog\/wp-content\/uploads\/2025\/08\/Picture4-1-300x147.png\" alt=\"\" width=\"492\" height=\"241\" srcset=\"https:\/\/www.softwaretraininginchennai.com\/blog\/wp-content\/uploads\/2025\/08\/Picture4-1-300x147.png 300w, https:\/\/www.softwaretraininginchennai.com\/blog\/wp-content\/uploads\/2025\/08\/Picture4-1.png 413w\" sizes=\"(max-width: 492px) 100vw, 492px\" \/><\/p>\n<ul>\n<li>To implement React routing, install react-router-dom, define routes using Route and Switch components, and use Link or NavLink to navigate between them without reloading the page. Considering we have the components App, About, and Contact in our application:<\/li>\n<\/ul>\n<h3><span style=\"color: #333399;\">What is the difference between React and Angular?<\/span><\/h3>\n<ul>\n<li>React is a JavaScript library, while Angular is a framework. React uses one virtual DOM and one-way data binding and has a small bundle size. Conversely, Angular uses real DOM and two-way data binding and is lighter and faster.<\/li>\n<\/ul>\n<p><strong>\u00a0<\/strong><\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>What is React.js? React is a JavaScript library for building user interfaces, particularly single-page applications.\u00a0It allows developers to create reusable UI components, manage state, and efficiently update the DOM. What are Components in React? Components are\u00a0independent and reusable bits of code. They serve the same purpose as JavaScript functions, but work in isolation and return [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[409],"tags":[426,428,427],"class_list":["post-1444","post","type-post","status-publish","format-standard","hentry","category-react-full-stack-development","tag-full-stack-react-questions","tag-interview-preparation-of-react-course","tag-react-question"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.2 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>React.js Interview Question | Maria Academy<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.softwaretraininginchennai.com\/blog\/react-js-interview-question\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"React.js Interview Question | Maria Academy\" \/>\n<meta property=\"og:description\" content=\"What is React.js? 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