ReactDOM is a core React package that provides DOM-specific methods to interact with and manipulate the Document Object Model (DOM), enabling efficient rendering and management of web page elements.

ReactDOM is used for:

• Rendering Components: Displays React components in the DOM.
• DOM Manipulation: Allows efficient DOM updates.
• Server-Side Rendering: Supports rendering on both client and server.
• React & DOM Bridge: Connects React with the browser’s DOM.

How to use ReactDOM?

To use the ReactDOM in any React web app, we must first install the react-dom package in our project. To install the react-dom package, use the following command.

// Installing
npm i react-dom 

After installing the package use the following command to import the package in your application file

// Importing
import ReactDOM from 'react-dom'

After installing react-dom, it will appear in the dependencies in the package. json file like:

"dependencies": {
    "react": "^18.2.0",
    "react-dom": "^18.2.0",
    "react-scripts": "5.0.1",
}

Important Methods of ReactDOM

• render(): This is one of the most important methods of ReactDOM. This function is used to render a single React component or several components wrapped together in a component or a div element. 
• findDOMNode(): This function is generally used to get the DOM node where a particular React component was rendered. This method is much less used, as the following can be done by adding a ref attribute to each component itself.
• unmountComponentAtNode(): This function is used to unmount or remove the React Component that was rendered to a particular container.
• hydrate(): This method is equivalent to the render() method but is implemented while using server-side rendering. 
• createPortal(): It allows us to render a component into a DOM node that resides outside the current DOM hierarchy of the parent component. 

Essential Functionalities of ReactJS

• ReactDOM.render() replaces the child of the given container if any. It uses a highly efficient diff algorithm and can modify any subtree of the DOM.
• React findDOMNode() function can only be implemented upon mounted components thus Functional components can not be used in findDOMNode() method.
• ReactDOM uses observables thus provides an efficient way of DOM handling.
• ReactDOM can be used on both the client-side and server-side.