What is React.js?

React.js is a popular open-source JavaScript library used for building user interfaces, particularly for single-page applications where the user interacts with a dynamic web page. Developed and maintained by Facebook (now Meta), it allows developers to create large web applications that can update and render efficiently in response to data changes without requiring a page reload.

Key features of React.js include:

• Component-Based Architecture: React lets you build encapsulated components that manage their state and then compose them to make complex UIs. Components can be reused, which helps in developing efficient and maintainable code.

• Virtual DOM: React uses a virtual DOM (a lightweight copy of the real DOM) to improve performance. When the state of an object changes, React updates only the relevant parts of the DOM, which leads to faster page rendering.

• Declarative Syntax: With React, you describe how your UI should look at any point in time, and React will automatically update and render the appropriate components when your data changes.

• JSX (JavaScript XML): React uses JSX, which is a syntax extension for JavaScript that looks similar to HTML. JSX makes it easier to write and understand the structure of the UI components.

React is often used in combination with other libraries or frameworks for tasks like routing, state management, or API calls, making it versatile for developing complex web applications.