Complete Guide to the Essential Configuration File next.config.js in Next.js

1. Role of the `next.config.js` File

The `next.config.js` file manages the configuration of a Next.js application, performing the following key roles:

• Build and development environment settings
• Extending Webpack configuration
• Setting environment variables
• Defining redirect and rewrite rules
• Image optimization settings

Through this file, you can customize various behaviors of the application.

2. Basic Structure

The basic structure of the `next.config.js` file is as follows:

// next.config.js
module.exports = {
  reactStrictMode: true,
  // additional settings
}

Add various settings inside the `module.exports` object.

3. Key Configuration Items

1. Enabling React Strict Mode

Activate React’s strict mode to detect potential issues in advance.

module.exports = {
  reactStrictMode: true,
}

2. Custom Webpack Configuration

You can extend or modify the default Webpack configuration of Next.js.

module.exports = {
  webpack: (config, { isServer }) => {
    // add custom Webpack settings
    return config;
  },
}

3. Setting Environment Variables

Manage configuration values required for development and deployment environments using environment variables.

module.exports = {
  env: {
    CUSTOM_API_ENDPOINT: process.env.CUSTOM_API_ENDPOINT,
  },
}

4. Redirect and Rewrite Settings

Define page redirect and URL rewrite rules.

module.exports = {
  async redirects() {
    return [
      {
        source: '/old-path',
        destination: '/new-path',
        permanent: true,
      },
    ]
  },
  async rewrites() {
    return [
      {
        source: '/api/:path*',
        destination: 'https://external-api.com/:path*',
      },
    ]
  },
}

5. Image Optimization Settings

Improve image loading speed by using Next.js’s image optimization feature.

module.exports = {
  images: {
    domains: ['example.com'],
  },
}

4. Advanced Configuration Examples

1. Adding Webpack Plugins

Extend the build process by using additional Webpack plugins.

const withPlugins = require('next-compose-plugins');
const withImages = require('next-images');

module.exports = withPlugins([withImages], {
  webpack: (config) => {
    // additional Webpack plugin settings
    return config;
  },
});

2. Custom Babel Configuration

Extend Babel settings in Next.js to use various JavaScript features.

module.exports = {
  babel: {
    presets: ['next/babel'],
    plugins: [['styled-components', { ssr: true }]],
  },
}

Conclusion

Understanding and utilizing the `next.config.js` file well can maximize the performance of your Next.js application and easily customize various settings. Refer to this guide to apply the necessary configurations to your project.

Check out more information in the Next.js official documentation.