What is React JS ?

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What is React JS ?

React JS is an open-source JavaScript library developed by Facebook for building user interfaces (UIs) for web applications. It provides a component-based approach to UI development, allowing developers to create reusable UI components and efficiently manage the state of their applications.

React focuses on the concept of building UIs as a composition of small, isolated, and reusable components. Each component represents a part of the user interface, which can have its own state and logic. These components can be composed together to form complex UI structures.

Key features of React JS include :

  1. Virtual DOM: React introduces a virtual representation of the DOM (Document Object Model) called the Virtual DOM. It creates a lightweight copy of the actual DOM, allowing React to efficiently update and render only the necessary components when the underlying data changes. This approach improves performance by minimizing unnecessary DOM manipulations.
  2. JSX: React uses JSX, which is a syntax extension that allows you to write HTML-like code within JavaScript. JSX makes it easier to describe the structure of UI components and their relationships. It provides a way to mix JavaScript logic and HTML-like syntax, making the code more readable and intuitive.
  3. Component-Based Architecture: React promotes a component-based architecture, where UIs are divided into reusable and independent components. Each component encapsulates its own logic and state, making it easier to reason about and maintain the codebase. Components can be nested within each other to create complex UI hierarchies.
  4. State Management: React provides a mechanism for managing and updating component state. State represents the internal data of a component that can change over time. By using the setState() method, developers can update the state of a component, triggering a re-render of the affected components. This helps keep the UI in sync with the data and ensures a responsive user experience.
  5. Unidirectional Data Flow: React follows a unidirectional data flow, where data flows from parent components to child components through props. Props (short for properties) are a way to pass data from one component to another. This approach ensures predictable and easy-to-debug data flow, as changes in the parent component are propagated down to its children.
  6. React Hooks: React Hooks were introduced in React 16.8 as a way to use state and other React features in functional components. Hooks provide a simpler and more concise way of managing state, lifecycle events, and side effects in functional components, eliminating the need for class components in many cases.


React JS has gained widespread popularity due to its efficiency, scalability, and developer-friendly features. It is widely used in the industry for building single-page applications (SPAs), complex web interfaces, mobile applications, and even desktop applications using frameworks like Electron.

React JS is a popular JavaScript library used for building user interfaces. It allows developers to create reusable UI components and efficiently manage the state of their applications. If you’re new to React JS, here are some key concepts and steps to get started:

Setting up the Development Environment:

  • Create a new React project: You can use a tool like Create React App (CRA) to set up a new React project quickly.

Understanding Components:

  • Components are the building blocks of a React application.
  • There are two types of components: functional components and class components.
  • Functional components are simple functions that return JSX (JavaScript XML).
  • Class components are ES6 classes that extend the React.Component class and have a render() method.




  • JSX is a syntax extension for JavaScript that allows you to write HTML-like code within your JavaScript files.
  • JSX elements represent the structure of the UI components.
  • You can use JSX expressions within curly braces {} to include dynamic content.

Rendering Components:

  • Use the ReactDOM.render() method to render your root component into the DOM.
  • Identify a root element in your HTML file where the React app will be mounted.


  • Props (short for properties) allow you to pass data from a parent component to its child components.
  • Props are read-only and cannot be modified by the child components.
  • Access props within a component using the props parameter in functional components or this.props in class components.


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