JavaScript Bundle Size Optimization: From 2MB to 200KB — A Practical Guide

JavaScript Bundle Size Optimization: From 2MB to 200KB A 2MB JavaScript bundle is a performance emergency. On a 4G connection it takes 2-3 seconds to download and parse — before your app renders anything. Here's a systematic approach to cutting bundle size dramatically. Step 1: Analyze Before You Optimize Never guess. Measure first. Webpack Bundle Analyzer npm install --save-dev webpack-bundle-analyzer # webpack.config.js const { BundleAnalyzerPlugin } = require ( 'webpack-bundle-analyzer' ) ; module.exports = { plugins: [ new BundleAnalyzerPlugin ({ analyzerMode: 'static' , openAnalyzer: false , reportFilename: 'bundle-report.html' , }) , ] , } ; Run npm run build and open bundle-report.html . You'll see a treemap of every dependency's contribution to your bundle. Common offenders: moment.js (330KB), lodash (70KB), date-fns (34KB per locale). Vite Bundle Analysis npm install --save-dev rollup-plugin-visualizer # vite.config.ts import { visualizer } from 'rollup-plugin-visualizer' ; ex