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Basic What is ReactJS?

React JS is a JavaScript library for building user interfaces, primarily used for creating single-page applications where data can change without reloading the page.

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Why ReactJS is Used?

We need React to efficiently build dynamic and interactive user interfaces with reusable components, which improves development speed and maintainability.

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How Does ReactJS work?

ReactJS works by using a component-based architecture to build UIs, where each component manages its own state and behavior. React uses a virtual DOM to efficiently update the actual DOM by only rendering the components that change. When the state or props of a component change, React compares the virtual DOM with the previous one, finds the differences, and updates the DOM efficiently. This approach ensures better performance and a smooth user experience.

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What are the features/advantage of ReactJS?

1. Component-Based Architecture: React builds the UI using small, reusable components, making the development and management of complex interfaces more efficient.
2. Virtual DOM: React maintains a virtual DOM to optimize performance by minimizing direct DOM manipulations. It updates only the parts of the DOM that have changed, improving speed.
3. JSX (JavaScript XML): React uses JSX, a syntax that combines JavaScript and HTML-like code, to create components more intuitively.
4. Unidirectional Data Flow: Data flows in one direction (from parent to child components), making the code predictable and easier to debug.
5. Hooks: Hooks, like useState and useEffect, allow you to manage state and side effects in functional components, simplifying the development process.
6. React Native: It provides the ability to build mobile apps using the same concepts and components as React for web development.
7. Declarative Syntax: React's declarative nature makes it easy to describe the UI based on the current application state.
8. Server-Side Rendering (SSR): React supports SSR, which enhances performance and SEO by rendering pages on the server before they reach the client.

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What is virtual DOM in React?

The Virtual DOM is a lightweight, in-memory representation of the real DOM in React. When a component’s state or props change, React updates the Virtual DOM instead of the real DOM immediately. It then compares the updated Virtual DOM with a snapshot of the previous one (a process called “diffing”) and identifies the minimum number of changes required. React then updates only the parts of the real DOM that have changed, improving performance by minimizing direct DOM manipulations.

\

Differentiate between real DOM and virtual DOM?

1. Real DOM:

• Refers to the actual DOM used in browsers.
• It is slow in updates because every change involves manipulating the entire tree, which can be expensive when large-scale changes occur.
• Direct interaction happens between the browser and the Real DOM.

1. Virtual DOM:

• A lightweight copy of the real DOM used by React.
• React uses it to optimize updates by first making changes to the Virtual DOM and then comparing it to the previous state (using a diffing algorithm).
• Only the differences are updated in the Real DOM, making the process faster and more efficient.
• It enhances the performance of web applications by minimizing direct manipulation of the Real DOM.

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What is JSX?

JSX is a syntax extension for JavaScript that allows you to write HTML-like code within JavaScript, making it easier to visualize the UI structure.

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How do browsers read JSX?

Browsers do not natively understand JSX, as it is not a standard JavaScript syntax. JSX is a syntax extension for JavaScript that looks similar to HTML but is meant for React. Here's how browsers handle it:

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1. JSX Transpilation: JSX is first transpiled (translated) into regular JavaScript using tools like Babel. During this process, JSX elements are converted into React.createElement() calls.

   \

2. React.createElement(): Once transpiled, JSX is represented as JavaScript objects describing the DOM tree. These objects are then processed by React, which renders them into actual DOM elements.

For example, JSX like:

const element =

Hello, world!

;

is transpiled to:

const element = React.createElement('h1', null, 'Hello, world!');

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3. JavaScript Execution: The browser's JavaScript engine runs this JavaScript code, and React manipulates the DOM based on the virtual DOM and state updates.

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What are components in React?

In React, components are the building blocks used to create user interfaces. They encapsulate parts of the UI and allow you to split the UI into independent, reusable pieces.

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How to create components in ReactJS?

1. Functional Components:

Functional components are the simplest form of components in React. They are JavaScript functions that return JSX (React’s syntax to write HTML-like code).

Example:

function MyComponent() { return ( ); } export default MyComponent;

\ 2. Class Components:

Class components are ES6 classes that extend React.Component. They can also hold and manage state and lifecycle methods.

Example:

import React, { Component } from 'react'; class MyComponent extends Component { render() { return ( ); } } export default MyComponent;

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What are the lifecycle Methods in Class Components

Lifecycle methods in class components are hooks that allow you to execute code at specific points during a component's lifecycle, including:

• componentDidMount: Called after the component is mounted.
• componentDidUpdate: Called after the component updates.
• componentWillUnmount: Called before the component unmounts.
• shouldComponentUpdate: Determines if a component should re-render.

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Explain the difference between functional and class components in React.

• Class Components: Use ES6 classes, can hold and manage state, and access lifecycle methods.
• Functional Components: Are stateless by default but can use state and other features through hooks like useState and useEffect.

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How do you pass data from parent to child?

Data is passed from parent to child components using props.

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Explain props and state in React with differences.

• Props (Properties):
• Passed from parent to child components.
• Immutable, meaning they cannot be modified by the child component.
• Used for data flow and configuration, allowing components to be reusable and flexible.
• Example: , where name is a prop.
• State:
• Managed within the component itself.
• Mutable, meaning it can be updated by the component using setState or useState.
• Used for dynamic data that changes over time (e.g., user input, form data).
• Example: const [count, setCount] = useState(0).

Key Differences:

• Props: Immutable, used for data passed down from parent components.
• State: Mutable, internal to the component, and can change based on interactions.

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What is the children prop in React?

The children prop in React is a special prop that allows components to pass other elements or components as its content. It is used to display whatever is placed between the opening and closing tags of a component.

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What is defaultProps in React?

defaultProps in React is a way to define default values for props in a component. If a prop is not provided by the parent component, the component will use the value specified in defaultProps.

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What is prop drilling and how to avoid it?

Prop drilling is basically a situation when the same data is being sent at almost every level due to requirements in the final level. The problem with Prop Drilling is that whenever data from the Parent component will be needed, it would have to come from each level, Regardless of the fact that it is not needed there and simply needed in last.

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What is the Purpose of Pure Components?

Pure Components in React optimize performance by implementing a shallow comparison on props and state, re-rendering only when there are changes, thus preventing unnecessary renders.

\n How to Create Elements in a Loop in React?

You can create elements in a loop in React by using JavaScript’s array methods, such as map().

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What is a key in React?

Keys are very important in lists for the following reasons:

• A key is a unique identifier and it is used to identify which items have changed, been updated or deleted from the lists
• It also helps to determine which components need to be re-rendered instead of re-rendering all the components every time. Therefore, it increases performance, as only the updated components are re-rendered

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Why are indexes for keys not recommended?

Keys are unique identifiers used in lists to help React identify which items have changed, been added, or removed. They are important for efficient re-rendering and to maintain the correct order of elements.

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Explain one-way data binding in React?

One-way data binding in React means that data flows in a single direction, from parent components to child components through props, ensuring predictable and controlled updates to the UI.

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What are hooks in React?

Hooks in React are special functions that allow developers to use state and other React features (such as lifecycle methods)

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Explain the useState hook in React?

The most used hook in React is the useState() hook. It allows functional components to manipulate DOM elements before each render. Using this hook we can declare a state variable inside a function but only one state variable can be declared using a single useState() hook. Whenever the useState() hook is used, the value of the state variable is changed and the new variable is stored in a new cell in the stack.

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What is useEffect() hook and how to manage side effects?

The useEffect() hook in React eliminates the side effect of using class based components. It is used as an alternative to componentDidUpdate() method. The useEffect() hook accepts two arguments where second argument is optional.

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What are custom hooks in React?

A custom hook is a function that encapsulates reusable logic using React hooks. It always starts with “use” to follow the convention.

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What is conditional rendering in React?

Conditional Rendering: In React, it means rendering different UI elements based on certain conditions, often using JavaScript operators like `if`, `ternary`, or `&&

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What is a Fragment?

A Fragment is a wrapper used in React to group multiple elements without adding extra nodes to the DOM.

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What is React Developer Tools?

React Developer Tools is a Chrome DevTools extension for the React JavaScript library. A very useful tool, if you are working on React.js applications. This extension adds React debugging tools to the Chrome Developer Tools. It helps you to inspect and edit the React component tree that builds the page, and for each component, one can check the props, the state, hooks, etc.

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How to use styles in ReactJS?

CSS modules are a way to locally scope the content of your CSS file. We can create a CSS module file by naming our CSS file as App.modules.css and then it can be imported inside App.js file using the special syntax mentioned below.

Syntax:

import styles from './App.module.css';

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What is react-redux?

Redux is a predictable state container for JavaScript applications. It helps you write apps that behave consistently, run in different environments (client, server, and native), and are easy to test. Redux manages an application’s state with a single global object called Store.

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What are benefits of using react-redux?

Redux solves the state transfer problem by storing all of the states in a single place called a store. So, managing and transferring states becomes easier as all the states are stored in the same convenient store. Every component in the application can then directly access the required state from that store.

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Explain the core components of react-redux.

• Single Source of Truth

The state of your whole application is stored in an object tree within a single-store.

A single state tree makes it easier to debug or inspect an application \n It gives you a faster development cycle by enabling you to persist in your app's navigation state

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• State Is Read-Only

The only way to change the state is to initiate an action, an object describing what happened.

This feature ensures that no events like network callbacks or views can change the state. They can only express an intent to change the state \n Actions are just plain objects; they can be logged, serialized, stored, and later replayed for debugging or testing purposes

\

• Changes are Made with Pure Functions

To specify how actions transform the state tree, you need to write pure reducers.

The user can return new state objects instead of mutating the previous stateThe user can start with a single reducer, and, as the app grows, can split it off into smaller reducers that manage specific parts of the state treeBecause reducers are just functions, it’s easy to control the order in which they are called, pass additional data, or even make reusable reducers

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What is context?

Context is a React feature that allows you to share state and other values between components without having to pass props manually at every level.

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What is context API?

Context API is used to pass global variables anywhere in the code. It helps when there is a need for sharing state between a lot of nested components. It is light in weight and easier to use, to create a context just need to call React.createContext(). It eliminates the need to install other dependencies or third-party libraries like redux for state management. It has two properties Provider and Consumer.

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Explain provider and consumer in ContextAPI?

A provider is used to provide context to the whole application whereas a consumer consume the context provided by nearest provider. In other words The Provider acts as a parent it passes the state to its children whereas the Consumer uses the state that has been passed.

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How to handle buttons in React?

Handling buttons in React is a straightforward process. Typically, buttons are used to trigger events, perform actions, or update state when clicked.

\

1. Basic Button with Event Handling In React, buttons can be rendered using the HTML element, and you can handle click events using the onClick attribute.

import React, { useState } from 'react'; function ButtonExample() { const [count, setCount] = useState(0); const handleClick = () => { setCount(count + 1); // Update the state when the button is clicked }; return ( ); } export default ButtonExample;

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2. Passing Arguments to Event Handlers If you need to pass arguments to your event handler, you can use an arrow function or bind the function.

function ButtonExample() { const handleClick = (name) => { console.log(Hello, ${name}); }; return ( handleClick('Luis')}>Say Hello ); }

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3. Preventing Default Behavior

   If a button has default behavior (like a form submission), you can prevent it using event.preventDefault().

function ButtonExample() { const handleSubmit = (event) => { event.preventDefault(); // Prevent form submission console.log('Form was submitted'); }; return (

Submit

); }

\ 4. Handling Multiple Buttons If you have multiple buttons, you can use the id or other identifying attributes to differentiate their actions.

function MultipleButtons() { const handleButtonClick = (action) => { console.log(${action} button clicked); }; return ( ); }

\

How to handle inputs in React?

In React, inputs are handled using controlled components, where the input's value is tied to the component's state through the value attribute, and updated using the onChange event. This allows for efficient management of inputs like text fields, checkboxes, and dropdowns.

const [inputValue, setInputValue] = useState(''); setInputValue(e.target.value)} />

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What is React Router?

React Router is a library that enables dynamic routing in React applications, allowing you to navigate between different components or pages without reloading the entire application.

\

Explain the components of React Router.

React Router is a popular library for handling routing in React applications, allowing you to manage navigation between different components or pages. The main components of React Router include:

\ 1. BrowserRouter

• Acts as the top-level container for routing and provides the routing context for the rest of the application.
• It uses the HTML5 history API to keep the UI in sync with the URL.

import { BrowserRouter, Route } from 'react-router-dom'; function App() { return ( ); }

\ 2. Routes and Route

• Routes is a wrapper that allows multiple routes to be defined.
• Route defines a path and the component that should render when the URL matches that path.

import { Routes, Route } from 'react-router-dom'; function App() { return ( } /> } /> ); }

\ 3. Link

• A component used for navigating between different routes without reloading the page (client-side routing).
• It replaces anchor () tags to ensure React Router can manage the navigation.

import { Link } from 'react-router-dom'; function Navigation() { return ( ); }

\ 4. useNavigate

• A hook that allows programmatic navigation (e.g., redirecting the user after a form submission).

import { useNavigate } from 'react-router-dom'; function Form() { const navigate = useNavigate(); const handleSubmit = () => { // After form submission, navigate to another page navigate('/success'); }; return Submit; }

\ 5. useParams

• A hook to access dynamic URL parameters.
• Useful for handling dynamic routes (e.g., displaying details of an item by its ID).

import { useParams } from 'react-router-dom'; function Product() { const { id } = useParams(); // Extract 'id' from URL return

Product ID: {id}

; }

\ 6. useLocation

• A hook to access the current location object, which contains information about the current URL (path, query parameters, etc.).

import { useLocation } from 'react-router-dom'; function CurrentLocation() { const location = useLocation(); return

Current Path: {location.pathname}

; }

\ 7. Navigate

• A component used for redirecting users to a different route.

import { Navigate } from 'react-router-dom'; function ProtectedRoute({ isAuthenticated }) { return isAuthenticated ? : ; }

\ 8. Outlet

• A placeholder component that renders child routes.
• Useful for creating layouts where the main content changes based on the route.

import { Outlet } from 'react-router-dom'; function Layout() { return (

Header

{/* Renders child routes */}

); }

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How does Routing work in ReactJS?

Routing in React is typically managed by libraries like React Router. It works by mapping URL paths to specific components. When a user navigates to a URL, the router displays the corresponding component without reloading the page, creating a seamless single-page application experience.

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How to implement data fetching in ReactJS?

Data fetching in React can be implemented using various methods, depending on your needs and the complexity of the application. The most common approach is to use React’s lifecycle methods or hooks like useEffect to fetch data from APIs or other sources.

\ 1. Using useEffect Hook

The useEffect hook allows you to perform side effects in functional components, including data fetching. This is the most common approach when working with functional components in React.

\

import React, { useState, useEffect } from 'react'; function DataFetchingComponent() { const [data, setData] = useState([]); const [loading, setLoading] = useState(true); const [error, setError] = useState(null); useEffect(() => { // Fetch data when the component mounts fetch('https://api.example.com/data') .then((response) => { if (!response.ok) { throw new Error('Network response was not ok'); } return response.json(); }) .then((data) => { setData(data); setLoading(false); // Data is fetched, stop loading }) .catch((error) => { setError(error.message); setLoading(false); }); }, []); // Empty dependency array ensures it only runs once when component mounts if (loading) return

Loading...

; if (error) return

Error: {error}

; return (

{data.map(item => (
• {item.name}
))}

); } export default DataFetchingComponent;

\ 2. Using axios for Data Fetching

Instead of using the native fetch API, you can use third-party libraries like Axios, which makes handling promises simpler and supports features like request cancellation.

\

import React, { useState, useEffect } from 'react'; import axios from 'axios'; function AxiosDataFetching() { const [data, setData] = useState([]); const [loading, setLoading] = useState(true); const [error, setError] = useState(null); useEffect(() => { // Fetch data using Axios axios.get('https://api.example.com/data') .then((response) => { setData(response.data); setLoading(false); }) .catch((error) => { setError(error.message); setLoading(false); }); }, []); if (loading) return

Loading...

; if (error) return

Error: {error}

; return (

{data.map(item => (
• {item.name}
))}

); } export default AxiosDataFetching;

\ 3. Using async/await for Cleaner Syntax

You can use async/await inside the useEffect hook for more readable asynchronous code.

\

import React, { useState, useEffect } from 'react'; function AsyncDataFetching() { const [data, setData] = useState([]); const [loading, setLoading] = useState(true); const [error, setError] = useState(null); useEffect(() => { const fetchData = async () => { try { const response = await fetch('https://api.example.com/data'); if (!response.ok) { throw new Error('Error fetching data'); } const data = await response.json(); setData(data); setLoading(false); } catch (error) { setError(error.message); setLoading(false); } }; fetchData(); }, []); if (loading) return

Loading...

; if (error) return

Error: {error}

; return (

{data.map(item => (
• {item.name}
))}

); } export default AsyncDataFetching;

\

Explain the difference between React and Angular?

• React is a JavaScript library focused on building user interfaces with a component-based architecture and uses a virtual DOM for efficient updates. It’s flexible and allows you to choose additional libraries for routing and state management.

• Angular is a full-fledged JavaScript framework that provides a complete solution for building web applications. It uses TypeScript, follows a model-view-controller (MVC) or model-view-view model (MVVM) architecture, and includes built-in tools for routing, state management, and dependency injection.

\

Create a Reusable Button Component with Props.

Button.js

import React from 'react'; import PropTypes from 'prop-types'; import './Button.css'; // Optional: for styling const Button = ({ onClick, type, children, className, disabled }) => { return ( {children} ); }; Button.propTypes = { onClick: PropTypes.func, type: PropTypes.oneOf(['button', 'submit', 'reset']), children: PropTypes.node.isRequired, className: PropTypes.string, disabled: PropTypes.bool, }; Button.defaultProps = { onClick: () => {}, type: 'button', className: '', disabled: false, }; export default Button;

\ Button.css

.btn { padding: 10px 20px; font-size: 16px; border: none; border-radius: 4px; cursor: pointer; transition: background-color 0.3s; } .btn:hover { background-color: #ddd; } .btn:disabled { cursor: not-allowed; opacity: 0.5; }

\ Usage Example:

import React from 'react'; import Button from './Button'; function App() { const handleClick = () => { alert('Button clicked!'); }; return (

Click Me Submit

); } export default App;

\

Create a form, email, pass, user, with validations.

Form.js

import React, { useState } from 'react'; const Form = () => { const [formData, setFormData] = useState({ email: '', password: '', username: '' }); const [errors, setErrors] = useState({ email: '', password: '', username: '' }); const [isSubmitted, setIsSubmitted] = useState(false); const handleChange = (e) => { const { name, value } = e.target; setFormData((prev) => ({ ...prev, [name]: value, })); }; const validate = () => { const { email, password, username } = formData; const newErrors = {}; if (!email) { newErrors.email = 'Email is required'; } else if (!/\S+@\S+\.\S+/.test(email)) { newErrors.email = 'Email address is invalid'; } if (!password) { newErrors.password = 'Password is required'; } else if (password.length < 6) { newErrors.password = 'Password must be at least 6 characters long'; } if (!username) { newErrors.username = 'Username is required'; } setErrors(newErrors); return Object.keys(newErrors).length === 0; }; const handleSubmit = (e) => { e.preventDefault(); if (validate()) { setIsSubmitted(true); // Handle form submission (e.g., API call) console.log('Form data submitted:', formData); } }; return (

Email: {errors.email &&

{errors.email}

}

Username: {errors.username &&

{errors.username}

}

Password: {errors.password &&

{errors.password}

}

Submit {isSubmitted &&

Form submitted successfully!

}

); }; export default Form;

\ Form.css

.error { color: red; font-size: 0.875em; } .success { color: green; font-size: 1em; } form { max-width: 400px; margin: auto; } div { margin-bottom: 15px; }

\ Usage:

import React from 'react'; import Form from './Form'; import './Form.css'; function App() { return (

Registration Form

); } export default App;

\ \

Intermediate What is the difference between controlled and uncontrolled components in React?

Controlled components in React have their form data managed by the component’s state, with updates handled via onChange events. Uncontrolled components manage their form data through the DOM, using refs to access values. Controlled components offer better control and synchronization, while uncontrolled components are simpler but less flexible.

\

Explain the lifecycle methods of components

A React Component can go through four stages of its life as follows.

• Initialization: This is the stage where the component is constructed with the given Props and default state. This is done in the constructor of a Component Class.

• Mounting: Mounting is the stage of rendering the JSX returned by the render method itself.

• Updating: Updating is the stage when the state of a component is updated and the application is repainted.

• Unmounting: As the name suggests Unmounting is the final step of the component lifecycle where the component is removed from the page.

  \

What is the difference between useState and useRef in React?

• useState: Creates state variables that trigger re-renders when updated.

• useRef: Creates a mutable reference that persists across renders without causing re-renders, commonly used to access DOM elements directly.

  \

What is StrictMode in React?

StrictMode is a tool for highlighting potential problems in a React application. It activates additional checks and warnings for its descendants, such as identifying unsafe lifecycle methods, detecting side effects in components, and ensuring best practices. StrictMode is a development-only feature and has no impact on production builds.

\

How Do You Modularize Code in a React Project?

Modularizing code in a React project involves organizing components, utilities, and styles into separate files and directories, making the codebase more maintainable and scalable. This can be achieved by:

• Using Component-based Structure: Each component has its own file.
• Creating Reusable Utility Functions: Keep utility functions in separate files.
• Using CSS Modules or Styled-components: Manage component-specific styles.
• Using Context for Global State: Group related states and logic together using Context API or state management libraries like Redux.

\

How to implement custom hooks in React?

Custom hooks in React are functions that start with use and allow you to encapsulate and reuse stateful logic across multiple components. They can call other hooks and return values such as state variables or functions. For example, a custom hook like useCounter can manage counter state and provide methods to increment, decrement, or reset the counter.

\

How does React implement reusability in components?

React implements reusability in components through several key features:

1. Component-Based Architecture: React allows you to build your UI with reusable, self-contained components. Each component can be used in multiple places, promoting consistency and reducing code duplication.
2. Props: Components accept inputs called props, which allow you to customize their behavior and appearance. This makes components highly reusable with different configurations.
3. Composition: React components can be composed together to build complex UIs from simpler components. This allows you to create reusable building blocks that can be combined in various ways.
4. Custom Hooks: Custom hooks enable you to extract and reuse stateful logic across multiple components. They provide a way to share functionality without duplicating code.
5. Higher-Order Components (HOCs): HOCs are functions that take a component and return a new component with additional props or behavior. This pattern helps reuse logic across different components.

\

What is a higher-order component (HOC) in React?

A Higher-Order Component (HOC) in React is a function that takes a component and returns a new component with additional props or behavior. It is used to enhance or reuse component logic across different components without modifying the original component. For example, an HOC can add loading functionality to a component by wrapping it and conditionally rendering a loading indicator.

\

What is code splitting in React?

Code splitting in React is a technique to improve performance by breaking up the application into smaller chunks that are loaded on demand. This is achieved using React.lazy and Suspense, which dynamically import components and show a fallback UI while they are being loaded.

\

What is Redux?

Redux is a state management library for JavaScript applications, often used with React. It provides a centralized store for all application state, making it easier to manage and debug complex states.

\

How Redux Works?

Redux works by following a unidirectional data flow:

1. Dispatch an Action: An action is dispatched based on user interaction or other triggers.
2. Reducer Updates State: The reducer function processes the action and returns a new state.
3. Store Holds State: The store saves the updated state and informs the application of changes, which causes a re-render of the components that rely on that state.

\

What is Redux Toolkit?

Redux Toolkit is a library that simplifies using Redux by providing tools like createSlice for reducing boilerplate code, configureStore for setting up the store, and built-in support for handling asynchronous logic. It streamlines state management in Redux and improves the development experience.

\

What is the use of the useCallback hook in React?

The useCallback hook is used to memoize a function, preventing it from being recreated on every render unless its dependencies change. This is useful for optimizing performance, especially when passing functions to child components.

\

What is the use of the useMemo hook in React?

The useMemo hook in React is used to memoize expensive calculations and prevent unnecessary re-computation. It recalculates the result only when its dependencies change, improving performance by avoiding re-renders of components with heavy computations.

\

What is React.memo and how is it used for performance optimization?

React.memo is a higher-order component (HOC) in React that optimizes performance by preventing unnecessary re-renders of a component. It works by memoizing the rendered output of a functional component and only re-renders it when its props change.

\

Explain provider and consumer in Context API.

In React's Context API, the Provider supplies data to components, while the Consumer accesses that data. The Provider wraps components and passes a value prop, and the Consumer retrieves that value. In functional components, the useContext hook is often used instead of Consumer for easier access to context.

\

Explain the Concept of Reconciliation in React.

Reconciliation is the process React uses to update the DOM by comparing the new and previous virtual DOM trees and applying the minimal set of changes needed to the real DOM.

\

What is the role of TypeScript in improving React code safety and scalability?

TypeScript improves React code safety and scalability by adding static type checking, which helps catch errors during development rather than at runtime. It ensures that components receive the correct props, enforces consistent data structures, and improves code maintainability. TypeScript also enhances scalability by making refactoring easier and improving code readability through type definitions.

\

Why is It Important to Test Your React Application?

Testing ensures that your React application works as expected. It helps catch bugs early, ensures that individual components function correctly, and maintains application stability as the codebase grows. Testing also provides confidence when refactoring or adding new features, as it can quickly identify unintended side effects.

\

What Would You Do If Your React Application is Rendering Slowly?

If a React application is rendering slowly, you can:

• Use React DevTools Profiler: Identify slow components and understand where rendering bottlenecks occur.
• Optimize with React.memo() or pureComponent: Prevent unnecessary re-renders of components that haven't changed.
• Lazy Load Components: Split the code and load components only when needed using React's lazy and Suspense.
• Debounce or Throttle Events: Reduce the frequency of event handler execution, especially for inputs or scrolling.
• Avoid Inline Functions/Objects: Inline functions or objects re-create on every render, causing child components to re-render.
• Use useCallback and useMemo: Optimize expensive calculations and function references in functional components.

\

Describe how to implement lazy loading in React using the lazy function and the Suspense component.

To implement lazy loading in React, use the React.lazy function to dynamically import components and the Suspense component to handle the loading state while the component is being loaded.

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1. Use React.lazy to load the component dynamically:

const LazyComponent = React.lazy(() => import('./LazyComponent'));

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2. Wrap the lazy-loaded component with Suspense, providing a fallback UI (e.g., a loader) while the component is being fetched:

import React, { Suspense } from 'react'; const App = () => ( Loading...