ihj04982/bundle-optimization

Bundle Optimization

Patterns to reduce initial bundle size, improve loading performance, and enable effective code-splitting.

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1. Avoid Barrel File Imports

Import directly from source files instead of barrel (index) files to avoid loading thousands of unused modules.

Bad (imports entire library):

import { Check, X, Menu } from 'lucide-react';
// Loads 1,583 modules, takes ~2.8s extra in dev

import { Button, TextField } from '@mui/material';
// Loads 2,225 modules

Good (direct imports):

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';

import Button from '@mui/material/Button';
import TextField from '@mui/material/TextField';

Alternative (Next.js 13.5+):

// next.config.js
module.exports = {
  experimental: {
    optimizePackageImports: ['lucide-react', '@mui/material'],
  },
};

Commonly affected: lucide-react, @mui/material, @mui/icons-material, @tabler/icons-react, react-icons, lodash, date-fns, rxjs.

Reference: How we optimized package imports in Next.js

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2. Dynamic Imports for Heavy Components

Use next/dynamic to lazy-load large components not needed on initial render.

Bad (Monaco bundles with main chunk ~300KB):

import { MonacoEditor } from './monaco-editor';

Good (loads on demand):

import dynamic from 'next/dynamic';

const MonacoEditor = dynamic(
  () => import('./monaco-editor').then((m) => m.MonacoEditor),
  { ssr: false },
);

---

3. Conditional Module Loading

Load large data/modules only when a feature is activated.

function AnimationPlayer({ enabled, setEnabled }: Props) {
  const [frames, setFrames] = useState<Frame[] | null>(null);

  useEffect(() => {
    if (enabled && !frames && typeof window !== 'undefined') {
      import('./animation-frames.js')
        .then((mod) => setFrames(mod.frames))
        .catch(() => setEnabled(false));
    }
  }, [enabled, frames, setEnabled]);

  if (!frames) return <Skeleton />;
  return <Canvas frames={frames} />;
}

The typeof window !== 'undefined' check prevents bundling for SSR.

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4. Defer Non-Critical Third-Party Libraries

Analytics, logging, and error tracking don't block user interaction. Load after hydration.

Bad (blocks initial bundle):

import { Analytics } from '@vercel/analytics/react';

Good (loads after hydration):

import dynamic from 'next/dynamic';

const Analytics = dynamic(
  () => import('@vercel/analytics/react').then((m) => m.Analytics),
  { ssr: false },
);

---

5. Optimize SVG Precision

Reduce SVG coordinate precision to decrease file size.

Bad: <path d="M 10.293847 20.847362 L 30.938472 40.192837" />

Good: <path d="M 10.3 20.8 L 30.9 40.2" />

Automate: npx svgo --precision=1 --multipass icon.svg

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Checklist

• [ ] Icon/component libraries imported directly, not via barrel files
• [ ] Heavy components (editors, charts) use dynamic imports
• [ ] Feature-gated modules loaded conditionally
• [ ] Analytics/logging/error tracking deferred to post-hydration
• [ ] SVG assets optimized with reduced precision