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# Bundling
Fix common bundling issues with third-party packages.
## Server-Incompatible Packages
Some packages use browser APIs (`window`, `document`, `localStorage`) and fail in Server Components.
### Error Signs
```
ReferenceError: window is not defined
ReferenceError: document is not defined
ReferenceError: localStorage is not defined
Module not found: Can't resolve 'fs'
```
### Solution 1: Mark as Client-Only
If the package is only needed on client:
```tsx
// Bad: Fails - package uses window
import SomeChart from 'some-chart-library';
export default function Page() {
return <SomeChart />;
}
// Good: Use dynamic import with ssr: false
import dynamic from 'next/dynamic';
const SomeChart = dynamic(() => import('some-chart-library'), {
ssr: false,
});
export default function Page() {
return <SomeChart />;
}
```
### Solution 2: Externalize from Server Bundle
For packages that should run on server but have bundling issues:
```js
// next.config.js
module.exports = {
serverExternalPackages: ['problematic-package'],
};
```
Use this for:
- Packages with native bindings (sharp, bcrypt)
- Packages that don't bundle well (some ORMs)
- Packages with circular dependencies
### Solution 3: Client Component Wrapper
Wrap the entire usage in a client component:
```tsx
// components/ChartWrapper.tsx
'use client';
import { Chart } from 'chart-library';
export function ChartWrapper(props) {
return <Chart {...props} />;
}
// app/page.tsx (server component)
import { ChartWrapper } from '@/components/ChartWrapper';
export default function Page() {
return <ChartWrapper data={data} />;
}
```
## CSS Imports
Import CSS files instead of using `<link>` tags. Next.js handles bundling and optimization.
```tsx
// Bad: Manual link tag
<link rel="stylesheet" href="/styles.css" />;
// Good: Import CSS
import './styles.css';
// Good: CSS Modules
import styles from './Button.module.css';
```
## Polyfills
Next.js includes common polyfills automatically. Don't load redundant ones from polyfill.io or similar CDNs.
Already included: `Array.from`, `Object.assign`, `Promise`, `fetch`, `Map`, `Set`, `Symbol`, `URLSearchParams`, and 50+ others.
```tsx
// Bad: Redundant polyfills
<script src="https://polyfill.io/v3/polyfill.min.js?features=fetch,Promise,Array.from" />
// Good: Next.js includes these automatically
```
## ESM/CommonJS Issues
### Error Signs
```
SyntaxError: Cannot use import statement outside a module
Error: require() of ES Module
Module not found: ESM packages need to be imported
```
### Solution: Transpile Package
```js
// next.config.js
module.exports = {
transpilePackages: ['some-esm-package', 'another-package'],
};
```
## Common Problematic Packages
| Package | Issue | Solution |
| --------------- | --------------- | --------------------------------------------------------------- |
| `sharp` | Native bindings | `serverExternalPackages: ['sharp']` |
| `bcrypt` | Native bindings | `serverExternalPackages: ['bcrypt']` or use `bcryptjs` |
| `canvas` | Native bindings | `serverExternalPackages: ['canvas']` |
| `recharts` | Uses window | `dynamic(() => import('recharts'), { ssr: false })` |
| `react-quill` | Uses document | `dynamic(() => import('react-quill'), { ssr: false })` |
| `mapbox-gl` | Uses window | `dynamic(() => import('mapbox-gl'), { ssr: false })` |
| `monaco-editor` | Uses window | `dynamic(() => import('@monaco-editor/react'), { ssr: false })` |
| `lottie-web` | Uses document | `dynamic(() => import('lottie-react'), { ssr: false })` |
## Bundle Analysis
Analyze bundle size with the built-in analyzer (Next.js 16.1+):
```bash
next experimental-analyze
```
This opens an interactive UI to:
- Filter by route, environment (client/server), and type
- Inspect module sizes and import chains
- View treemap visualization
Save output for comparison:
```bash
next experimental-analyze --output
# Output saved to .next/diagnostics/analyze
```
Reference: https://nextjs.org/docs/app/guides/package-bundling
## Migrating from Webpack to Turbopack
Turbopack is the default bundler in Next.js 15+. If you have custom webpack config, migrate to Turbopack-compatible alternatives:
```js
// next.config.js
module.exports = {
// Good: Works with Turbopack
serverExternalPackages: ['package'],
transpilePackages: ['package'],
// Bad: Webpack-only - migrate away from this
webpack: (config) => {
// custom webpack config
},
};
```
Reference: https://nextjs.org/docs/app/building-your-application/upgrading/from-webpack-to-turbopack