Optimizing Package Bundling in Next.js – Analyze, Reduce, and Control Dependencies

Introduction

Bundling external packages efficiently plays a key role in application performance. Next.js automatically bundles packages used in Server Components and Route Handlers, but you can further optimize this process using advanced tools and configuration options.

Analyzing JavaScript Bundles

The @next/bundle-analyzer plugin helps you visualize and inspect the size of your application bundles. You can use it to identify large dependencies and decide whether to remove, split, or lazy-load them.

Installation

npm i @next/bundle-analyzer

Configuration

const withBundleAnalyzer = require('@next/bundle-analyzer')({
  enabled: process.env.ANALYZE === 'true',
})

module.exports = withBundleAnalyzer({})

Generating the Report

ANALYZE=true npm run build

This will open three visual reports in your browser, showing bundle sizes and dependencies.

Optimizing Package Imports

Some libraries, like icon sets, export hundreds of modules. To avoid unnecessary overhead, use optimizePackageImports to only include what you use:

experimental: {
  optimizePackageImports: ['icon-library'],
}

Next.js automatically optimizes some libraries, so you don’t need to include them manually. See the full list in the documentation.

Opting Packages Out of Server Bundling

Packages used in Server Components and Route Handlers are bundled by default. To exclude specific packages from bundling, use serverExternalPackages:

serverExternalPackages: ['package-name']

Next.js also maintains a list of packages that are automatically excluded due to compatibility concerns.

Conclusion

By analyzing bundles, optimizing imports, and controlling server-side dependencies, you can significantly improve the performance of your Next.js application. These strategies help reduce JavaScript payloads, speed up load times, and deliver a better user experience.