React Virtual DOM Explained in Simple English

If you are using React or learning React, you must have heard of the term “Virtual DOM”. Now what is a Virtual DOM, and why does React use it?

Real DOM

First things first, DOM stands for “Document Object Model”. The DOM in simple words represents the UI of your application. Everytime there is a change in the state of your application UI, the DOM gets updated to represent that change. Now the catch is frequently manipulating the DOM affects performance, making it slow.

What makes DOM manipulation slow?

The DOM is represented as a tree data structure. Because of that, the changes and updates to the DOM are fast. But after the change, the updated element and it’s children have to be re-rendered to update the application UI. The re-rendering or re-painting of the UI is what makes it slow. Therefore, the more UI components you have, the more expensive the DOM updates could be, since they would need to be re-rendered for every DOM update.

Virtual DOM

That’s where the concept of virtual DOM comes in and performs significantly better than the real DOM. The virtual DOM is only a virtual representation of the DOM. Everytime the state of our application changes, the virtual DOM gets updated instead of the real DOM.

How is Virtual DOM faster?

When new elements are added to the UI, a virtual DOM, which is represented as a tree is created. Each element is a node on this tree. If the state of any of these elements changes, a new virtual DOM tree is created. This tree is then compared or “diffed” with the previous virtual DOM tree.

source: https://www.oreilly.com/library/view/learning-react-native/9781491929049/ch02.html

How does React use Virtual DOM

Now that you have a fair understanding of what a Virtual DOM is, and how it can help with performance of your app, lets look into how React leverages the virtual DOM.

React render() function

render() is where the UI gets updated and rendered. render() is the required lifecycle method in React. You can learn more about React lifecycle methods in detail from my blog post.

Recap

  • Frequent DOM manipulations are expensive and performance heavy.
  • Virtual DOM is a virtual representation of the real DOM.
  • When state changes occur, the virtual DOM is updated and the previous and current version of virtual DOM is compared. This is called “diffing”.
  • The virtual DOM then sends a batch update to the real DOM to update the UI.
  • React uses virtual DOM to enhance its performance.
  • It uses the observable to detect state and prop changes.
  • React uses an efficient diff algorithm to compare the versions of virtual DOM.
  • It then makes sure that batched updates are sent to the real DOM for repainting or re-rendering of the UI.

Software Consultant, Author, Speaker, React Native|React|GraphQL Dev & Indian Classical Musician http://adhithiravichandran.com/