bundle-barrel-imports

## Avoid Barrel File Imports Import directly from source files instead of barrel files to avoid loading thousands of unused modules. **Barrel files** are entry points that re-export multiple modules (e.g., `index.js` that does `export * from './module'`). Popular icon and component libraries can have **up to 10,000 re-exports** in their entry file. For many React packages, **it takes 200-800ms just to import them**, affecting both development speed and production cold starts. **Why tree-shaking doesn't help:** When a library is marked as external (not bundled), the bundler can't optimize it. If you bundle it to enable tree-shaking, builds become substantially slower analyzing the entire module graph. **Incorrect (imports entire library):** ```tsx import { Check, X, Menu } from 'lucide-react' // Loads 1,583 modules, takes ~2.8s extra in dev // Runtime cost: 200-800ms on every cold start import { Button, TextField } from '@mui/material' // Loads 2,225 modules, takes ~4.2s extra in dev ``` **Correct (imports only what you need):** ```tsx import Check from 'lucide-react/dist/esm/icons/check' import X from 'lucide-react/dist/esm/icons/x' import Menu from 'lucide-react/dist/esm/icons/menu' // Loads only 3 modules (~2KB vs ~1MB) import Button from '@mui/material/Button' import TextField from '@mui/material/TextField' // Loads only what you use ``` **Alternative (Next.js 13.5+):** ```js // next.config.js - use optimizePackageImports module.exports = { experimental: { optimizePackageImports: ['lucide-react', '@mui/material'] } } // Then you can keep the ergonomic barrel imports: import { Check, X, Menu } from 'lucide-react' // Automatically transformed to direct imports at build time ``` Direct imports provide 15-70% faster dev boot, 28% faster builds, 40% faster cold starts, and significantly faster HMR. Libraries commonly affected: `lucide-react`, `@mui/material`, `@mui/icons-material`, `@tabler/icons-react`, `react-icons`, `@headlessui/react`, `@radix-ui/react-*`, `lodash`, `ramda`, `date-fns`, `rxjs`, `react-use`. Reference: [How we optimized package imports in Next.js](https://vercel.com/blog/how-we-optimized-package-imports-in-next-js)