optimizePackageImports in Next.js

optimizePackageImports in Next.js

Tiger Abrodi's photo
Tiger Abrodi
·

3 min read

Table of contents

The Barrel File Problem

Many libraries (especially icon/component libraries) use "barrel files", files that re-export many modules from a single entry point.

For example, if you do import { AlertIcon } from 'lucide-react', you're actually importing through a barrel file that might contain thousands of other icon exports. Even though you only want one icon, the JavaScript runtime has to process ALL exports, which can take 200-800ms or even seconds.

Why it's a Performance Issue

  • Every require() or import has overhead in JavaScript.

  • In development: Slows down initial startup and hot module reloading

  • In production: Especially impacts serverless environments where cold starts are frequent

  • Some libraries have up to 10,000 re-exports in their barrel files!

How optimizePackageImports Works

You enable it in next.config.js for specific packages:

module.exports = {
  experimental: {
    optimizePackageImports: ["lucide-react", "my-lib"],
  },
};

Next.js analyzes the barrel file of these packages. When it sees import { AlertIcon } from 'lucide-react', it automatically transforms it to import directly from the specific module file. It's like changing import { AlertIcon } from 'lucide-react' to import AlertIcon from 'lucide-react/dist/icons/alert' under the hood.

When to Use It

You should consider using optimizePackageImports when:

  • You're using large icon libraries (lucide-react, @tabler/icons-react)

  • You're using component libraries with many exports (@mui/material)

  • You notice slow development server startup times

  • You're concerned about cold start times in production

  • Your hot module reloading feels sluggish

Real Performance Improvements

  • Development: 15-70% faster startup times

  • Build time: ~28% faster builds

  • Cold starts: Up to 40% faster

  • For example, @material-ui/icons went from 10.2s to 2.9s in development

How to Spot When It's Needed

  • Your node_modules contains packages with large index.js files that have many exports (use bundle analyzer).

  • You're using popular icon or UI component libraries

  • Your development server takes several seconds to start up

  • Your builds are slower than expected

  • You notice performance issues when importing from large libraries

  • You can check the import time by adding console.time() before and after your imports

Example using console time:

console.time("import");
import { AlertIcon } from "lucide-react";
console.timeEnd("import");

The beauty

The beauty is that it's automatic. You opt-in the packages you want to optimize, and Next.js handles the rest.

Not for your own barrel files

optimizePackageImports is specifically for optimizing EXTERNAL packages from node_modules, not your own barrel files.

This is a confusion many have.

For your own barrel files in your project, you should avoid them completely.

// Using a barrel file
import { Button, Card, TextField } from "@/components";

It's better for performance to import directly:

// Direct imports - better performance
import Button from "@/components/Button";
import Card from "@/components/Card";
import TextField from "@/components/TextField";

The optimizePackageImports feature is specifically designed to help with third-party packages where you can't control their structure, especially large ones like:

  • Icon libraries (lucide-react, @tabler/icons)

  • UI component libraries (@mui/material)

  • Large utility libraries

If you're seeing performance issues with your own barrel files, the solution is to refactor to use direct imports rather than trying to optimize the barrel files themselves.

Next.js