ReactJS

React, also known as Reactjs or React.js, is a free and open-source front-end JavaScript library for building user interfaces or UI components. It is maintained by Meta and a community of individual developers and companies. React can be used as the foundation for single-page applications. Its goal is to be fast, scalable, and simple. React manipulates the DOM in memory and updates the browser's DOM only when changes are needed.

React was developed by Jordan Walke, a software engineer at Facebook. It was first released in May 2013. React's component-based architecture allows developers to break down complex UIs into smaller, reusable pieces. Each component has its own logic and appearance. This approach promotes code reusability and makes it easier to manage and maintain large applications. React uses a virtual DOM, which is an in-memory representation of the actual DOM. When a component's state changes, React updates the virtual DOM first and then efficiently calculates the minimum number of changes needed to update the real DOM. This virtual DOM diffing process significantly improves performance.

React is declarative, meaning developers describe what the UI should look like for a given state, and React handles the updates. This makes code more predictable and easier to debug. It supports one-way data binding, where data flows in a single direction, from parent components to child components. This unidirectional data flow further enhances predictability and simplifies debugging. React is widely adopted for building modern web applications, from simple websites to complex enterprise-level platforms. Its ecosystem includes many supporting libraries and tools for routing, state management, and more.