How to Reduce Next.js Bundle Size by 60 Percent: Complete Optimization Guide

A 500KB JavaScript bundle takes 4 plus seconds to parse on mobile. Here is how to cut it down.

Step 1: Analyze Your Bundle

Install @next/bundle-analyzer, add to next.config.js and run ANALYZE=true npm run build. Look for the biggest chunks.

Step 2: Dynamic Imports for Heavy Components

const Chart = dynamic(() => import('./Chart'), {
  loading: () => <Skeleton />,
  ssr: false
});

Step 3: Fix Barrel File Imports

Barrel files (index.ts that re-exports everything) prevent tree shaking. Import directly from the source file instead.

Step 4: Tree Shake Lodash

Replace import { debounce } from lodash with import debounce from lodash/debounce.

Step 5: Use Server Components

Server components send zero JavaScript. Move data fetching and static rendering to server components.

Step 6: Lazy Load Below the Fold

Anything below the fold should be dynamically imported or lazy loaded.

Results

These optimizations typically reduce First Load JS from 300-500KB to 100-150KB.

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