React and ReactDOM are both fundamental parts of the React ecosystem, but they serve distinct roles.
React is, at its core, a library for building user interfaces. It introduces the concept of components, which allow developers to craft reusable and self-contained UI elements. These components define how a user interface should appear based on given inputs (props and state). React operates with a virtual representation of the DOM, known as the Virtual DOM, which is an abstraction of the actual browser’s DOM. By working with this abstraction, React can determine the most efficient way to update the browser’s DOM when data changes, leading to efficient and performant UI updates.
ReactDOM, on the other hand, acts as the glue between React’s Virtual DOM and the actual browser’s DOM. It provides the means to render React components into the DOM. The primary method it offers is `ReactDOM.render()`, which is used to take a React component and render it into a specified DOM node. Additionally, ReactDOM provides utilities for directly interacting with the DOM, like `findDOMNode()` (though its use is often discouraged in favor of more “React-ish” approaches). Importantly, ReactDOM is specific to web browsers.
The reason for this separation is React’s design philosophy to be platform-agnostic. While ReactDOM deals with web-specific rendering, there are other renderers like React Native (for mobile apps) or ReactVR (for virtual reality) that leverage the core React library to target different platforms. By decoupling the core definitions of components from the platform-specific rendering logic, React becomes a versatile solution for various environments.
While React provides the tools and concepts to define component-based user interfaces, ReactDOM handles the task of rendering those interfaces in a web environment. Together, they form the foundation of React web applications.
