component-based JavaScript library in react.pptx

React JS
ReactJS is a component-based JavaScript
library used to build dynamic and interactive
user interfaces.
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React JS
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It simplifies the creation of single-page applications (SPAs) with a focus on
performance and maintainability.
 It is developed and by Facebook & now maintained by community developer.
 Uses a virtual DOM for faster updates.
 Supports a declarative approach to designing UI components.
 Ensures better application control with one-way data binding.

What is react component ?
03
 components are the building blocks of a React application
 A component is essentially a reusable, self-contained piece of UI.
 React allows you to break down a complex UI into smaller, manageable pieces
 React offers two main types of components: functional components and class
components.

First react project using vite
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 Vite is a modern frontend build tool that provides a faster development
experience & development server experience for modern web projects .
npm create vite@latest

Why vite ?
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 Vite is a fast, modern build tool with Hot Module Replacement features
created by the founder of Vue.js Evan You ,
 designed for optimized development and production workflows.
Top Reasons to Use Vite
⚡ 1. Ultra-Fast Development Server
 ite uses native ES modules to serve files directly to the browser.

Why vite ?
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 No bundling during development = instant startup.
 Changes in code are reflected almost instantly with Hot Module Replacement
(HMR).
⚡ 1. Uses Rollup under the hood for efficient bundling.
 Automatically splits code, removes unused code (tree-shaking), and minifies output.
📦 2. Optimized Production Build

Why vite ?
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🚀 3. Out-of-the-Box Modern Features
 ES6+ support, TypeScript, JSX, CSS modules, PostCSS, and more — no extra
config needed.
 Built-in support for .env files, dynamic imports, and asset handling.
🎯 4. Minimal Config & Easy Setup
 Create a working project in seconds using:
npm create vite@latest

Why vite ?
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💡 5. Great DX (Developer Experience)
 Cleaner error messages.
 Fast feedback loop = higher productivity.
 Plugins and integrations are simpler.
🧩 6. Framework Agnostic, But Optimized
 Works great with Vue 3, React, Svelte, Lit, Solid, and even plain JavaScript.
 Official templates for each framework.

Why vite ?
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🔄 7. Fast Refresh & HMR
 When you save a file, only the module that changed is updated in the browser.
 This leads to a smoother and faster dev workflow compared to traditional
bundlers.
🌍 8. Strong Community & Ecosystem
 Backed by Evan You (Vue’s creator).
 Active plugin ecosystem.
 Popular among frontend frameworks and open source tools.

Run React Project
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npm run dev npx vite
OR
For build
npm run build npx vite build
OR

vite.config.js
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npm run dev npx vite
OR
For build
npm run build npx vite build
OR

React Project Structure
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Distribution Node Modules
Public Src
main.jsx node_modules
.gitignore App.jsx

useRef Hook
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built-in React Hook that returns a mutable reference object (ref) that persists
across renders
Accessing and manipulating DOM elements without triggering re-renders.
Persisting values across renders without causing re-renders.
Storing previous state values to compare changes between renders
Optimizing performance by avoiding unnecessary state updates

useRef Hook Working With Attribute
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useRef Working With Input Element
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[Hook] useRef Working With CSS Class
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[Hook] useRef Working With Persisted Mutable Property
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The value of mutable property is only
updated
component is not re-rendered

[Hook] useRef Caching Expensive Computation
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useRef holds a persistent value that survives across renders
but doesn’t cause re-renders when updated
When can use it
 When you need to re-use result multiple times without re-rendering
 Cache expensive computations
 Store previous values
 Avoid recalculating something unnecessarily
 Preventing reinitialization of complex objects
Where can use it
 For API Calling
 Avoiding duplicate form submissions

[Hook] useRef Caching Expensive Computation
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If state change occure then re-render the component
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The React useState Hook allows us to track state in a function component.
State generally refers to data or properties that need to be tracking in an application
When to Use useState
 We need a simple state management solution.
 We component has state that changes over time.
 The state does not require complex updates or dependencies.
[Hook] useState Understading Inside

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State
Holds all data
view

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[Hook] useState Working With Immutable Object
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Immutability : state can’t modify or mutate directly , but
previous object can be change by creating and replacing by new
object
React can’t track prevoius state if you change the state directly
React can’t re-render the component if you change the state directly

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[Hook] useState Working With Immutable Array
 don't modify or mutate directly
 Make new copy using spread (...) operator
 use setState process for update

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useState Spread Operator And Immutability Principle
Main
Object/Origi
nal DOM
Clone Object
1/Virtual
DOM1
Clone Object
3/Virtual
DOM3
Clone Object
2/Virtual DOM2
diffting
Reconciliation

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 The spread operator (...) in React.js is a powerful feature that simplifies working with
arrays and objects, particularly when managing component state.
 Used to expand the iterable items , The three dots syntax (...) is used
 spread operator (...) is used for cloning, merging, or passing props, arrays, or objects
in a concise and readable way to a component
 React state should be immutable . It allows you to create shallow copies of arrays and
objects, making it easier to update them without directly modifying the original data.
 It’s a JavaScript feature, not unique to React

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 The spread operator helps create new objects or arrays with the desired changes, leaving
the original data untouched.
 In React, it's crucial to maintain immutability of state.
 Directly modifying state can lead to unexpected behavior and hinder performance
optimizations.
Immutability:

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[Hook] useEffect understanding arguments and uses
🔸 useEffect Has Two Arguments
1. Callback Function — () => { ... }
 This is the function that runs after the component renders.
 You perform your side effects here — like calling an API,
setting up intervals, adding event listeners, etc.
useEffect(() => {
console.log("Component mounted");
}, []);
📍 Only runs once, like componentDidMount.

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🔸 useEffect Has Two Arguments
2. Dependency Array — [dep1, dep2, ...] (optional)
 This array tells React when to run the effect.
 React compares the current values with the previous ones
 If any dependency has changed, the effect runs again.
 If the array is empty ([]), the effect runs only once on mount.
 If you omit the array, the effect runs after every render.
useEffect(() => {
console.log("Count changed:");
}, [1]);
📍 Runs every time count changes.
useEffect : perform side effects in function components, like data fetching,
subscriptions, DOM manipulation, etc.

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[Hook] useEffect understanding arguments and uses promises style
Api Call
Do’t go next step
If previous step fails

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[Hook] useEffect understanding arguments and uses , async await process
Api Call
Do’t go next step
If previous step fails

component-based JavaScript library in react.pptx

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