What is React.js

1. What is React j.s
React is a free and open source JavaScript library. It's used for Building user interfaces(UIs) specifically for single-page Applications(SPA). Created by Facebook(now meta) in 2013,it's allows Developers create large web application that can change data without Reloading the page.

React helps developers create:

• Websites
• Single Page Applications (SPA)
• Dashboards
• E-commerce apps
• Social media apps
• Mobile apps (with React Native)

Why React was Created

• React was created to solve problems developers faced while building larger and dynamic web applications.

Before React, developers updated HTML manually using JavaScript.

Example:
document.getElementById("title").innerHTML = "welcome";

When the application become larger:

• Code became messy
• Updating UI became difficult
• Performance issues happened

React solving this by introducing :

Components,Virtual DOM,State management,Reusable UI

2. What is the different between library and Framework ?

• The primary difference between a library and a framework is Inversion of Control(IOC) in short, When you use a library, your are the in charge; When you use a framework, the framework is in charge.

Use a library when:

• You need flexibility
• Small project
• Specific feature only
• Want custom architecture

Use a framework when:

• Building large applications
• Need standard structure
• Team collaboration
• Faster large-scale development

Simple Concept

Library = Helper-(It helps your code)

Framework = Foundation-(Your app runs inside it)

3. What is Build Tool

• A build tool is a software utility that automates the process of converting source code.which typically includes JSX, modern JavaScript (ES6+), and CSS—into a optimized, production-ready format that web browsers can understand

Why Build Tools Are Needed

Modern web applications use:

• Multiple files
• React components
• TypeScript
• SCSS
• Images
• APIs
• Modules

Browsers cannot directly understand everything.

For example:

-Browsers do not understand JSX directly
-Browsers do not understand TypeScript directly

Build tools convert them into normal JavaScript, HTML, and CSS.

Common Examples by Language

1. Java - Apache Maven, Gradle

2. JavaScript - npm,webpack,vite

3. C/C++ - Make, CMake

4. Python - Poetry, pip

4. What is vite

• Vite (pronounced “veet”) is a modern frontend build tool used to create fast web applications.It offers instant server startup and lightning-fast Hot Module Replacement (HMR), making it a popular replacement for tools like Create React App.

Why Vite Was Created

Older build tools like:

Webpack

became slow for large applications.

Problems:

-Slow startup
-Slow rebuilds
-Slow hot reload

Vite was created to solve these speed problems.

Vite helps developers:

-Start projects quickly
-Run development servers
-Bundle files
-Optimize applications