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What is React? (Live Playground)

React is an open-source JavaScript library created by Facebook that enables developers to build user interfaces (UIs) for web applications. It focuses on making UI development more efficient, maintainable, and scalable. React is component-based, which means that the UI is divided into reusable pieces called components. These components can be combined and manipulated to build complex and dynamic applications.

Key Features of React

1. Components

React components are the building blocks of a React application. They allow you to create reusable, modular, and self-contained UI elements that can be easily maintained and updated.

function Greeting(props) {
return <h1>Hello, {}!</h1>;

2. Declarative

React allows you to describe how you want your UI to look at any given moment and automatically updates the UI when the underlying data changes. This makes your code more readable and easier to reason about.

function App() {
const [count, setCount] = useState(0);

return (
<button onClick={() => setCount(count + 1)}>Increase</button>
<p>Count: {count}</p>
Live Playground, Try it Yourself

3. Virtual DOM

React uses a virtual representation of the actual DOM called the Virtual DOM. When changes are made in the UI, React first updates the Virtual DOM, then calculates the differences between the new and old Virtual DOM (known as "diffing"). It then updates only the actual DOM elements that have changed, which leads to faster rendering times and improved performance.

4. Unidirectional Data Flow

React follows a unidirectional data flow, where data is passed down from parent components to child components through properties called "props". This makes it easier to track and manage the flow of data in your application.

function ParentComponent() {
const userName = 'John Doe';

return <ChildComponent name={userName} />;

function ChildComponent(props) {
return <p>Welcome, {}!</p>;

Benefits of Using React

  • Improved performance: The Virtual DOM enables faster and more efficient updates to the UI.
  • Reusability: Component-based architecture allows you to reuse components, which can save time and reduce code duplication.
  • Easier maintenance: React's declarative nature and unidirectional data flow make it easier to understand and maintain large applications.
  • Strong community: React has a large and active community of developers, which means you can find a wealth of resources, libraries, and tools to help you build your application.
  • Cross-platform development: With React Native, you can use your React knowledge to build native mobile applications for iOS and Android.


In summary, React is a powerful JavaScript library that simplifies the process of building user interfaces for web applications. Its component-based architecture, declarative nature, and efficient handling of updates make it an excellent choice for developing modern web applications.