Best Practices for React App Performance Optimization

React’s efficiency in building complex user interfaces is undeniable, but as app complexity grows, performance can become a challenge. In this comprehensive guide, I will cover some key techniques for React performance optimization with practical examples.

Learn how to fine-tune your app for maximum speed, responsiveness, and efficiency, to ensure a smooth user experience.

Fundamentals of React Performance

Before we start looking at ways to improve performance, it’s important to grasp the basics of how React works and what affects its performance. Let’s take a look at the main ideas related to React performance.

Virtual DOM :

React uses a Virtual DOM (VDOM) to improve performance significantly. The Virtual DOM is a simplified and in-memory version of the actual DOM. When something changes in your app, React first updates the Virtual DOM. Then, it compares this updated version with the previous one in a process called “reconciliation.”

Through examining the differences between the two versions, React figures out the best way to apply these changes to the real DOM. This method allows React to group and reduce the number of updates, which means it makes fewer changes to the DOM.

By batching and minimizing these updates, React reduces unnecessary DOM manipulations, resulting in faster rendering and a smoother user experience.

React Performance Optimization Techniques

Lets explore the 7 best techniques to optimize performance of your React application:

#1. Use React .memo() :

React.memo() is a higher-order component that helps to optimize the performance of functional react components by preventing unnecessary re-renders. It works by remembering the last rendered output of a component and only re-rendering it if its props have changed.

When a functional component wrapped with React.memo() receives the same props as its previous render, React skips rendering the component and reuses the last output, thus saving time and resources.

import React from 'react';

// A simple functional component
const MyComponent = (props) => {
  console.log('Rendering MyComponent');
  return <div>{props.value}</div>;
};

// Wrapping the component with React.memo() to prevent unnecessary re-renders
const MemoizedComponent = React.memo(MyComponent);

const App = () => {
  const [count, setCount] = React.useState(0);
  const [text, setText] = React.useState('Hello');

  return (
    <div>
      <button onClick={() => setCount(count + 1)}>Increment Count</button>
      <button onClick={() => setText('Hi')}>Change Text</button>
      <MemoizedComponent value={text} />
    </div>
  );
};

export default App;

In this example, MyComponent will only re-render if the value prop changes. When you click the “Increment Count” button, the count state changes, but since value remains the same, MyComponent does not re-render

Real-World Example: Imagine a dashboard with multiple widgets, each displaying data fetched from an API. If a user interacts with one widget (e.g., filtering data), using React.memo() can prevent other widgets from unnecessary re-renders, making the dashboard more responsive and improving overall performance.

#2. Implement PureComponent :

If you’re working with class components, you might want to consider using PureComponent instead of the regular Component. A PureComponent performs a shallow comparison of both the component’s props and state to determine if a re-render is necessary.

If the values haven’t changed, the PureComponent skips the render process, which can improve performance by reducing unnecessary re-renders.

For example, imagine you have a list component that displays a list of items and a search bar. The list component doesn’t need to re-render when the search bar’s input changes.

By using PureComponent, the list component will only re-render if the list items actually change, not when the search input changes. This helps keep your app responsive and efficient, especially with larger and more complex UIs.

import React, { PureComponent } from 'react';

class MyComponent extends PureComponent {
  // Component logic
}

#3. Use Key Prop in Lists :

When creating lists of components, make sure to include a unique key for each one. React uses these keys to quickly recognize and manage the elements when changes happen. If you don’t use the right keys or forget to include them, it can cause performance issues.

<ul>
  {items.map((item) => (
    <li key={item.id}>{item.name}</li>
  ))}
</ul>

For example, imagine a to-do list application where users can add, remove, or reorder tasks. If each task doesn’t have a unique key, React might struggle to keep track of which task is which, leading to incorrect updates or slower rendering.

This can make the app less responsive and more prone to bugs. Unique keys ensure that each task is correctly managed, improving overall performance and user experience.

#4. Avoid Inline Function Definitions :

Try not to define functions inside the render method, because it can cause the program to re-render more often than needed. Instead, create functions outside the render method or use arrow functions for shorter event handlers.

class MyComponent extends React.Component {
  handleClick = () => {
    // Handle click
  }

  render() {
    return <button onClick={this.handleClick}>Click me</button>;
  }
}

For example, if you have a Button component that changes state onClick, defining the click handler inside the render method will create a new function every time the button is clicked, potentially leading to excessive re-renders. By defining the handler outside the render method, you keep the function instance stable, making the component more efficient.

#5. Use Code Splitting :

Code splitting helps break your web application into smaller parts, so that only the code necessary for a specific route or feature is loaded. This makes the initial loading time shorter and improves overall application performance.

import React, { lazy, Suspense } from 'react';

const LazyComponent = lazy(() => import('./LazyComponent'));

function MyComponent() {
  return (
    <Suspense fallback={<div>Loading...</div>}>
      <LazyComponent />
    </Suspense>
  );
}

For example, imagine an e-commerce site with multiple features like a product catalog, a user profile, and a checkout process. Without code splitting, all of these features would load simultaneously, which could slow down the initial load time.

By using code splitting, the site only loads the code for the product catalog when the user first visits the site. As the user navigates to their profile or the checkout page, the necessary code for those features is loaded on demand.

This results in a quicker startup time and a smoother user experience, especially on slower connections or devices.

#6. Optimize Expensive Renders with useMemo and useCallback

The useMemo hook helps you save the results of expensive calculations so you don’t have to redo them every time. On the other hand, useCallback saves functions to avoid creating new ones when they aren’t needed. You should use these hooks when you want to make your important components run faster.

import React, { useMemo, useCallback } from 'react';

function MyComponent({ data }) {
  const expensiveResult = useMemo(() => calculateExpensive(data), [data]);
  const handleClick = useCallback(() => doSomethingWithResult(expensiveResult), [expensiveResult]);

  return (
    <div>
      <button onClick={handleClick}>Click me</button>
    </div>
  );
}

Imagine you have a component that filters a large list of items based on user input. Using useMemo to cache the filtered list prevents the app from redoing the filter operation every time the component updates.

Similarly, if you have a button in a child component that triggers a function passed from the parent, using useCallback ensures the function isn’t recreated every time the parent renders, which can avoid unnecessary re-renders of the child component.

#7. UseTransition Hook

The useTransition hook allows React to focus on important updates, like user inputs, before handling less urgent ones. As a result, the user experience becomes smoother. By delaying non-urgent updates, `useTransition` reduces interruptions in the user interface, which helps to enhance performance, especially in complex apps that require a lot of rendering.

import React, { useState, useTransition } from 'react';

function MyComponent() {
  const [state, setState] = useState(initialState);
  const [isPending, startTransition] = useTransition();

  function handleClick() {
    startTransition(() => {
      setState(newState); // This state update is marked as a transition
    });
  }

  return (
    <>
      {/* Your component JSX */}
      <button onClick={handleClick}>Update State</button>
      {isPending && <div>Loading...</div>}
    </>
  );
}

Final Words

With proper implementation of these 7 techniques, you can expect your web app to be faster and more efficient than before. You can also consider using react devtools. It provides a set of tools to inspect the structure of a React app, monitor its performance, and identify potential issues.

If you are a non-tech person, this might seem overwhelming, in which case you should consider hiring an experienced React developer to handle it for you.

FAQ

What Reactjs Uses to Improve the Performance?

To improve app’s performance ReactJS uses something called the Virtual DOM.

Is ReactJS Good for Big Projects?

Yes, ReactJS is well-suited for big projects. It offers a component-based architecture, making it easier to manage complex UIs, reuse code, and scale applications efficiently.

Does React Lazy Improve Performance?

Yes, React.lazy improves react app’s performance by enabling code-splitting. It loads components only when they are needed, reducing the initial load time and improving overall app speed.

What is React Developer Tools?

React Developer Tools is a browser extension that helps developers inspect, debug, and optimize React applications by providing tools to view component structures, state, and performance.

How to Measure the Performance of a React Application?

You can measure React application’s performance by using tools like React Developer Tools, which monitors component render times, or by utilizing browser performance tools to analyze load times and rendering efficiency.