260223:1415 20260223 nextJS & nestJS Best pratices

.agents/skills/next-best-practices/bundling.md

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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