React App Performance Optimization: The Definitive Guide

React App Performance Optimization: The Definitive Guide

React App Performance Optimization. Techniques to speed up your React App. DOM in React is a standard that defines how you get, update or manipulate HTML elements. The Virtual DOM is React’s a local copy of the HTML DOM.

Techniques to speed up your React App

How is the UI rendered in React?

In React, your UI is rendered by updating something called DOM (Document Object Model). In basic layman terms, DOM resembles a tree-like structure of objects and nodes.

In React, however, HTML is not the root node of a DOM. In fact, it is only one single node from Javascript’s prototype chain so that it gets the functions to calculate styles, properties or manipulate the individual nodes.

In simpler terms, DOM in React is a standard that defines how you get, update or manipulate HTML elements.

The React DOM knows how to render a page but it is not so intelligent to keep track of each node and components which are updating.

So, let’s say you have a list of 10 items on your SPA (Single Page Application) and you have to update one of them when your user interacts with UI. With DOM, you will end up updating all the components as the entire list will get re-rendered.

That’s where the concept of Virtual DOM comes into play. The Virtual DOM is React’s a local copy of the HTML DOM.

Let’s go back to our list example and figure out how Virtual DOM will let React renders the UI.

When the user interacts with UI, React would create a copy in the form of Virtual DOM and updates the UI after comparing the real DOM with the virtual DOM. In this way, the item which needs to be updated will update without affecting other items.

What’s bad about the Virtual DOM?

In the above section, you read about the good parts of Virtual DOM.

Now, let’s be familiar with the bad parts of Virtual DOM which are single-handedly responsible for many performance issues in React.

React leverages a diff algorithm in order to minimize the operations to be done at nodes. However, the algorithm in its own sense is not perfect.

For instance, let’s take a look at the GIF given below which resembles a react DOM tree. Let’s say that the values of the nodes in yellow have changed, and need to be updated.

As you can see above, React goes on rendering the whole subtrees instead of rendering the relevant component. When these unnecessary renders are left idle in a React application, they can eat up unnecessary CPU and memory resources which can be fatal for your React application. This is why they are called Wasted Renders.

When it comes to Virtual-DOM, about half of performance-related issues in Reactjs are originated from:

  • Redundant processing in components that do not update the DOM
  • Diff Algorithm keeps on updating leaf nodes that do not need to be updated
  • Heavy CPU computation due to Diff algorithm updating components

web-development react software-development javascript

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