Next.js Automatic Code Splitting: Improve Performance with Optimized Chunks

Introduction

Next.js is a framework for building server-side rendered React applications that offers many features to improve performance, including automatic code splitting. Automatic code splitting allows Next.js to divide your code into small, optimized chunks and only load the necessary code for each page, reducing load times and improving performance.

To get started with automatic code splitting in Next.js, follow these steps:

Step 1: Create a new Next.js app

Create a new Next.js app using the following command in your terminal:

npx create-next-app my-app

This will create a new Next.js app in a folder named my-app.

Step 2: Create multiple pages

Create multiple pages in your app by creating new files in the pages directory. For example, create two new files named index.js and about.js with the following code:

pages/index.js

function HomePage() {
  return (
    <div>
      <h1>Welcome to my app!</h1>
    </div>
  )
}

export default HomePage

pages/about.js

function AboutPage() {
  return (
    <div>
      <h1>About us</h1>
    </div>
  )
}

export default AboutPage

Step 3: Start the development server

Start the development server using the following command in your terminal:

npm run dev

This will start the development server and make your app available at http://localhost:3000.

Step 4: Inspect the network requests

Open your app in a web browser and open the developer tools. Navigate to the “Network” tab and refresh the page. You should see that the JavaScript files for each page are loaded separately.

Step 5: Test automatic code splitting

To test automatic code splitting, add a large third-party library to one of your pages. For example, you can add the moment.js library to your about.js page by installing it with the following command:

npm install moment

Then, update your about.js page to use the moment.js library:

pages/about.js

import moment from 'moment'

function AboutPage() {
  const date = moment().format('MMMM Do YYYY, h:mm:ss a')
  return (
    <div>
      <h1>About us</h1>
      <p>Current time: {date}</p>
    </div>
  )
}

export default AboutPage

Step 6: Inspect the network requests again

Refresh your app in the web browser and inspect the network requests again. You should see that the moment.js library is loaded separately from your main app code, and only on the about page.

By following these steps, you have successfully implemented automatic code splitting in your Next.js app. This feature will help you reduce load times and improve performance by only loading the necessary code for each page.