What is ReactJS DOM? Virtual DOM, DOM Router, Methods, How to Install?

Anyone who is familiar with React or has written React code must probably have heard of Virtual DOM. However, many don’t understand how it works or why to use it. 

Hence, let’s understand what is React DOM, React virtual DOM, and much more in detail. 

Topics Covered

• What is React DOM?

• What is React Virtual DOM?

• What is React DOM Router?

• React DOM vs Virtual DOM

• React DOM Methods

• React DOM vs React Router DOM

• How to Install React DOM?

Whenever a user sends a request to open a webpage, the browser receives an HTML document from the server for that page. It constructs a tree-like logical structure from the HTML to show the requested page to the user. That tree-like structure is known as the Document Object Model or DOM.

In simple terms, DOM in React is a structured representation of HTML elements present in a webpage and highlights the entire UI of an application. It comprises a node of each UI element in the web document. It allows developers to edit content through JavaScript, its structured format enables them to choose specific targets, and the code gets much easier to work with. 

When there is any change in the state of an app UI, DOM is also updated to represent the change. It is manipulated and rendered with each modification to update the UI, which slows it down and hampers its performance. So, if there are many UI components and complex DOM structures, updates can be expensive as the app needs to be re-rendered every time.

If you know about JavaScript, you might have seen people using the ‘getElementById()’ or ‘getElementsByClassName()’ method to edit the content of the DOM. For every change in the state of the application, the DOM needs to get updated to reflect the same modification in the UI. 

This may not seem like a major issue, and it has worked fine till now. However, what if a DOM contains a large number of nodes and the web elements have numerous attributes and styling? With DOM represented as a tree, updating it may not be costly, but there will be a lot of algorithms on trees to make modifications. 

The expenses will increase because every time DOM is updated, the modified element and its children will be rendered again and again to update the UI of the web page. Each time there is an update in a component, the DOM will have to be updated, and the UI components have to be re-rendered. 

Updating React DOM goes beyond changing the content, as there is a lot associated with it. CSS will have to be recalculated, and changing layouts involve complex algorithms, which affects the performance. Therefore, React adopts a different approach to deal with this and uses Virtual DOM.

ReactJS Virtual DOM is a lightweight copy of the actual DOM. We can also call it a virtual representation or version of the DOM. For every object present in the original DOM, VDOM has an object for it. 

However, it doesn’t have the power to change the layout of the document directly. Unlike DOM, where manipulation is slow, VDOM enables faster manipulation as there is nothing drawn on the screen. 

So, whenever there is a change in the state of an app, the virtual DOM gets updated first rather than the real DOM. 

• React VDOM is the virtual or digital representation of the real DOM.

• React updates changes in VDOM first and then syncs them with the actual one.

• Virtual DOM in ReactJS is like a blueprint of a machine. One can make changes in the blueprint, but they won’t be applied to the machine.

• VDOM can also be referred to as a programming concept, where the digital representation of the user interface is in the memory and synced with the real DOM by a library. This is called reconciliation.

• VDOM speeds up the process by dividing the page into small elements rather than updating it completely. 

Let’s know about the difference between DOM and Virtual DOM in React:

Let’s start by understanding the React Router. 

React Router is a standard library for routing among different view components in React applications. It keeps the UI in sync with the URL and allows to define the view to display for the specified URL. 

There are three primary React Router packages, namely:

React Router

Includes the core functionality of React Router, which includes route-matching algorithms and hooks.

React Router DOM

Comprises everything in React Router along with a few DOM-specific APIs.

React Router Native

Contains everything in React Router with a few React Native-specific APIs.

The primary function of React Router DOM is to implement dynamic routing in a web app. In traditional routing architecture, the routing is managed in a configuration outside of the running app. However, React Router DOM supports component-based routing based on the requirements of the app and platform.  

The routing process includes directing users to different pages according to their actions. ReactJS Router is frequently used to develop Single-page applications and to define multiple routes. Social media platforms, such as Instagram and Facebook, use React Router to render multiple views.

ReactJS provides a declarative API for creating components, but it also provides a set of DOM methods that can be used to interact with the underlying DOM elements. 

These DOM methods in React allow developers to manipulate the DOM elements created by components. 

Here are some of the commonly used ReactJS DOM methods:

ReactDOM.render() 

This method is used to render a React component into a specified DOM node. It takes two arguments, the first is the React component to be rendered and the second is the DOM node where the component will be rendered.

ReactDOM.findDOMNode()

This method returns the DOM node associated with a given React component. It can be used to access the underlying DOM node and manipulate its properties.

ReactDOM.createPortal()

This method is used to render a React component into a different part of the DOM tree. It is useful for rendering components that need to be positioned outside of the current DOM hierarchy.

ReactDOM.unmountComponentAtNode()

This method is used to unmount a React component from a specified DOM node. It takes a single argument, which is the DOM node from which the component will be unmounted.

React Router is a core package that includes standard components and functionalities to implement routing in React apps. On the other hand, React Router DOM is a special package used only in web browser-based app development. It exports React Router as a dependency and has additional DOM bindings. 

To work on web applications, React Router DOM is the best option as it contains the necessary components and features essentials for routing in a web app. Moreover, it installs React Router as a dependency, so one doesn’t have to re-install and import anything directly from the React Router. 

On React Native mobile applications, React Router Native is sufficient in the same way React Router DOM is enough for web apps. Therefore, there is no need to import React Router package as React Router DOM offers all major and essential functionalities.

The ReactJS library is usually distributed through a package manager, such as npm or Yarn. 

Here are the steps to install ReactJS and its dependencies using npm:

1. Install Node.js and npm on your machine, if you haven't already done so. You can download Node.js from the official website (https://nodejs.org/).

2. Open a terminal or command prompt and create a new project directory. Navigate to this directory in your terminal.

3. Run the following command to initialize a new Node.js project and create a package.json file:

npm init -y

4. Install the ReactJS and ReactDOM packages as dependencies by running the following command:

npm install react react-dom

This will install the latest versions of ReactJS and ReactDOM packages in your project, along with their dependencies.

5. Once the installation is complete, you can start building your ReactJS application.

Note: You don't need to install any separate package for ReactJS DOM methods, as they are included in the React and ReactDOM packages that you installed in Step 4.

1. How many Virtual DOM are in React?

React JS uses one virtual DOM for operation.

2. Why is virtual DOM faster?

A virtual DOM is a lightweight copy of the real DOM, and everything else is the same between the two. So, it can’t manipulate on-screen elements, and in case of any change, it updates the corresponding nodes rather than the entire tree. 

Hence, making it faster and more efficient. Moreover, because of no direct access or change to DOM elements in virtual DOM, it is extremely fast. 

3. Why React uses virtual DOM?

React uses virtual DOM as a strategy to compute small DOM operations while re-rendering the UI. It also provides a mechanism that takes away the manual DOM operations from developers and helps them to write predictable code. 

4. What is the difference between ReactJS and React DOM?

ReactJS is a JavaScript library for building user interfaces, while React DOM is a package that provides methods for rendering React components into the DOM. ReactJS provides a declarative API for creating components, while React DOM provides methods for interacting with the underlying DOM elements created by those components.

5. How do I access the underlying DOM node of a React component?

You can use the ReactDOM.findDOMNode() method to access the underlying DOM node of a React component. This method returns the DOM node associated with a given React component.

6. How do I render a React component into a specific DOM element?

You can use the ReactDOM.render() method to render a React component into a specific DOM element. This method takes two arguments: the React component to be rendered, and the DOM element where the component should be rendered.

7. Can I use ReactJS without using React DOM?

No, you cannot use ReactJS without using React DOM. React DOM provides the necessary methods for rendering React components into the DOM.

8. How do I unmount a React component from the DOM?

You can use the ReactDOM.unmountComponentAtNode() method to unmount a React component from the DOM. This method takes a single argument, which is the DOM node where the component is currently mounted.

9. What is the purpose of ReactDOM.createPortal()?

ReactDOM.createPortal() is a method that allows you to render a React component into a different part of the DOM tree. This is useful for rendering components that need to be positioned outside of the current DOM hierarchy. For example, you can use ReactDOM.createPortal() to render a modal dialog box outside of the main app container.