𝗛𝗼𝘄 𝘁𝗼 𝗥𝗲𝗱𝘂𝗰𝗲 𝗝𝗮𝘃𝗮𝗦𝗰𝗿𝗶𝗽𝘁 𝗕𝘂𝗻𝗱𝗹𝗲 𝗦𝗶𝘇𝗲 𝗯𝘆 𝟳𝟬%

Most web apps send too much code. The average page loads 1.7 MB of JavaScript. Developers use only 35% of the code they ship.

Smaller bundles improve your speed. You improve Largest Contentful Paint and Time to Interactive.

Follow these 10 steps to cut your size.

  1. Tree shaking Remove unused exports. Use ES Module syntax. Add "sideEffects": false to your package.json. This removes about 18% of unused code.

  2. Code splitting Split your code into smaller chunks.

  3. Dynamic imports Load code only when users need it. Use lazy loading for routes. This can cut initial bundle size by 28%.

  4. Image optimization Use URL-based transforms from a CDN. Stop using large inline SVGs.

  5. Dependency auditing Check package sizes with npx bundle-phobia. • Use date-fns (13KB) instead of moment.js (67KB). • Use lodash-es instead of lodash. • Use dayjs (2KB) for simple dates.

  6. Minification Remove extra spaces and characters. Most bundlers do this automatically.

  7. Compression Use Brotli instead of Gzip. Brotli is 15% to 25% better at shrinking files.

  8. Dead code elimination Remove code that the computer can never reach.

  9. Lazy loading components Delay loading parts of the page that are below the fold.

  10. Polyfill pruning Use @babel/preset-env. Only ship polyfills for the browsers your users actually use.

Stop making these mistakes:

  • Shipping development builds. Always use NODE_ENV=production.
  • Importing whole libraries. Import specific functions instead.
  • Skipping analysis. Use webpack-bundle-analyzer to see your large chunks.
  • Forgetting compression. Uncompressed files are 5x larger than Brotli files.

Track your progress with these targets:

  • Total JS size: Under 120 KB.
  • LCP: Under 2.5s.
  • TTI: Under 3.5s.

Focus on tree shaking, code splitting, and auditing first. These three steps often provide a 50% to 70% reduction in one sprint.

Source: https://dev.to/kui_luo/how-to-reduce-your-javascript-bundle-size-by-70-in-10-steps-3j1g