ReactJS, also known as React, is a popular JavaScript library for building user interfaces. It is also referred to as a front-end JavaScript library. It was developed by Facebook and is widely used for creating dynamic and interactive web applications. In this article, we’ll explore the key concepts of React.

What is React ?
React is a JavaScript library for building user interfaces (UIs) on the web. React is a declarative, component based library that allows developers to build reusable UI components and It follows the Virtual DOM (Document Object Model) approach, which optimizes rendering performance by minimizing DOM updates. React is fast and works well with other tools and libraries.

Prerequisite of React
For learning React first you have a clear understanding of HTML, CSS and JavaScript. As React is a JavaScript library and uses most of its concept so you really have to understands the major concepts of it.

HTML and CSS
JavaScript and ES6
JSX (Javascript XML) & Babel
Node+Npm
Git and CLI (Command Line Interface).

How does React work?
React operates by creating an in-memory virtual DOM rather than directly manipulating the browser’s DOM. It performs necessary manipulations within this virtual representation before applying changes to the actual browser DOM. React is efficient, altering only what requires modification.

Features of React
React is one of the most demanding JavaScript librarys because it is equipped with a ton of features which makes it faster and production-ready. Below are the few features of React.

1. Component-Based Architecture
React provides the feature to break down the UI into smaller, self-contained components. Each component can have its own state and props.

2. JSX (JavaScript Syntax Extension)
JSX is a syntax extension for JavaScript that allows developers to write HTML-like code within their JavaScript files. It makes React components more readable and expressive.

const name="GeekforGeeks";
const ele = <h1>Welcome to {name}</h1>;

3. Virtual DOM
React maintains a lightweight representation of the actual DOM in memory. When changes occur, React efficiently updates only the necessary parts of the DOM.

4. One-way Data Binding
One-way data binding, the name itself says that it is a one-direction flow. The data in react flows only in one direction i.e. the data is transferred from top to bottom i.e. from parent components to child components. The properties(props) in the child component cannot return the data to its parent component but it can have communication with the parent components to modify the states according to the provided inputs.

5. Performance
As we discussed earlier, react uses virtual DOM and updates only the modified parts. So , this makes the DOM to run faster. DOM executes in memory so we can create separate components which makes the DOM run faster.

6. Components
React divides the web page into multiple components as it is component-based. Each component is a part of the UI design which has its own logic and design as shown in the below image. So the component logic which is written in JavaScript makes it easy and run faster and can be reusable.

7. Single-Page Applications (SPAs)
React is recommended in creating SPAs, allowing smooth content updates without page reloads. Its focus on reusable components makes it ideal for real-time applications.

ReactJS Lifecycle
Every React Component has a lifecycle of its own, lifecycle of a component can be defined as the series of methods that are invoked in different stages of the component’s existence. React automatically calls these methods at different points in a component’s life cycle. Understanding these phases helps manage state, perform side effects, and optimize components effectively.