React JS ReactDOM

ReactDOM is a core React package that provides methods to interact with the Document Object Model, or DOM. This package allows developers to access and modify the DOM. It is a package in React that provides DOM-specific methods that can be used at the top level of a web app to enable an efficient way of managing DOM elements of the web page. ReactDOM provides the developers with an API containing the various methods to manipulate 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",
}

Why is ReactDOM used?

Earlier, React developers directly manipulated the DOM elements, which resulted in frequent DOM manipulation, and each time an update was made, the browser had to recalculate and repaint the whole view according to the particular CSS of the page, which made the total process consume a lot of time.

To solve this issue, React brought into the scene the virtual DOM. The Virtual DOM can be referred to as a copy of the actual DOM representation that is used to hold the updates made by the user and finally reflect it over to the original Browser DOM at once, consuming much less time. 

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.

Use Case

• Rendering the elements and react app to the root DOM element.
• Hydrating the components rendering on serverside with the client-side intractivity.
• Managing the DOM for dynamic user interface.