Migrate from Webpack to Vite Without Breaking Everything

This migration isn't going to be the smooth "few hours" process that blog posts promise. Every project I've worked on hit different weird issues that took way longer than expected to resolve.

The Reality Check Nobody Mentions

Legacy component libraries break in unexpected ways. Element UI pre-2.15, Material-UI before 5.0, and basically any NPM package that hasn't been updated since 2020 will shit the bed with import errors that take forever to track down. The official Vite docs mention this but don't prepare you for how painful it actually is.

Custom Webpack loaders don't transfer over. Webpack loaders don't work in Vite at all - you need to rewrite them as Vite plugins or find completely different approaches. Custom SVG processing, weird CSS transformations, and custom asset handling all need to be rebuilt. I spent two days rewriting a custom loader before realizing there was already a plugin for it.

Dynamic imports with variables are limited. Webpack lets you do import(\./locales/${lang}.js`)but Vite is pickier. You'll need to useimport.meta.glob()` instead, which I learned the hard way after getting "Cannot resolve module" errors for three hours straight.

Automated Tool Reality Check

The automated migration tool handles basic config conversion but misses a lot of edge cases:

npx @originjs/webpack-to-vite <project-path>

What it handles well:

• Basic Webpack config conversion to Vite config
• Package.json dependency updates
• HTML entry point creation
• Simple plugin mappings

What it fucks up:

• Custom loaders (you're rewriting them from scratch)
• Complex plugin configurations that don't have Vite equivalents
• Environment variable naming (every REACT_APP_* variable needs manual conversion to VITE_*)
• Import path resolution issues that only break at runtime, naturally

Time Estimates Based on Project Complexity

Marketing timelines are bullshit. Here's what actually happens:

• Simple React app: Usually takes 2-3 days, but will stretch to a week if you have any dependencies from before 2021
• Medium complexity with custom build steps: Expect at least a week, maybe longer if you hit compatibility issues with your precious webpack loaders
• Enterprise codebases: Can take weeks or months depending on how much custom tooling some architect built 3 years ago

Major time sinks you'll encounter:

1. Environment variable conversion - Every process.env.REACT_APP_* needs to become import.meta.env.VITE_* across your codebase
2. CSS import issues - CSS modules need explicit .module.css extensions or they just disappear
3. Plugin replacement research - Finding Vite equivalents for your webpack plugins, some don't exist yet
4. Testing everything again - The automated tool often misses edge cases that break in production

Framework-Specific Issues

Each framework has its own special ways to break during migration:

React projects:

• Asset imports like import logo from './logo.svg' sometimes need explicit ?url suffix for no good reason (thanks, Vite!)
• Babel plugins like babel-plugin-import just don't exist in Vite land, so you're hunting for Rollup alternatives that probably don't work the same way
• Hot reload stops working randomly and you'll restart the dev server 50 times a day like it's 2015 again

Vue projects:

• Vue 2 support is limited, migrate to Vue 3 first or suffer
• Single File Component imports break in unexpected ways
• Template compilation differences can change component behavior subtly

TypeScript projects:

• Built-in support works well but behaves differently than ts-loader
• Path mapping sometimes fails to resolve properly (because of course it does)
• Type-only imports need explicit import type syntax now

Performance Reality Check

Production builds stay the same speed - don't migrate expecting faster builds. The improvement is development experience, not build performance.

Development improvements you'll see:

• Dev server startup drops from 30+ seconds to under 5 seconds
• Hot reload becomes actually instant when it works correctly
• Better error messages and debugging experience
• Simpler configuration that's easier to understand and modify

Potential downsides:

• Initial page loads might be slower due to ES modules loading individually
• Production builds can be slower until you optimize chunks properly
• Memory usage increases in development due to serving unbundled files
• Different bundling behavior can expose edge cases in your code

Don't bother if your webpack setup already works fine. This migration is about developer happiness, not making things faster in production.

Copy these commands, but your project will break in its own special way.

Step 1: Create a Branch (Don't Be an Idiot)

git checkout -b webpack-to-vite-migration
git push -u origin webpack-to-vite-migration

This migration breaks things in unexpected ways. Working on a branch saves you from having to explain to your team why the main branch won't build anymore and why Jenkins is sending angry emails to everyone.

Step 2: Remove Webpack Dependencies

Start by removing webpack packages and installing Vite:

## Remove webpack core packages
npm uninstall webpack webpack-cli webpack-dev-server webpack-bundle-analyzer
npm uninstall mini-css-extract-plugin html-webpack-plugin copy-webpack-plugin

## Install Vite base
npm install --save-dev vite

## Add framework plugin (React example):
npm install --save-dev @vitejs/plugin-react

If you have a complex webpack setup, don't remove everything at once like a fucking maniac. Check your webpack.config.js for custom plugins first - you'll need to find Vite alternatives or rewrite them entirely (spoiler: there probably isn't a Vite equivalent).

Step 3: Create HTML Entry Point

Vite expects an HTML file as the entry point instead of a JavaScript file. Create index.html in your project root:

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8" />
  <meta name="viewport" content="width=device-width, initial-scale=1.0" />
  <title>Your App</title>
</head>
<body>
  <div id="app"></div>
  <script type="module" src="/src/main.js"></script>
</body>
</html>

Make sure the script src path matches your actual entry file location or you'll get a blank page with no obvious error message.

Step 4: Create Vite Configuration

Create vite.config.js with basic settings:

import { defineConfig } from 'vite'
import react from '@vitejs/plugin-react'
import path from 'path'

export default defineConfig({
  plugins: [react()],
  
  server: {
    port: 3000,
    // host: true, // Add only if you need network access
  },
  
  resolve: {
    alias: {
      '@': path.resolve(__dirname, 'src'),
    },
  },
  
  // Environment variable compatibility
  define: {
    'process.env.NODE_ENV': JSON.stringify(process.env.NODE_ENV),
  }
})

Things that will break:

• Global SCSS imports: If your webpack config includes global SCSS files, import them in your main entry file or they disappear like they never existed
• Path aliases: Match these to your existing webpack aliases or you'll get "Cannot resolve module" errors on every fucking import
• Server host settings: Only enable host: true if you need external network access - I debugged this for 6 hours before realizing the issue was the network config (thanks, Docker)

Step 5: Update Package Scripts

Replace webpack commands with Vite equivalents in your package.json:

{
  "scripts": {
    "dev": "vite",
    "build": "vite build",
    "preview": "vite preview"
  }
}

Step 6: Convert Environment Variables

This requires updating every environment variable reference in your codebase. Every process.env.REACT_APP_* needs to become import.meta.env.VITE_*:

// Webpack format
const apiUrl = process.env.REACT_APP_API_URL

// Vite format 
const apiUrl = import.meta.env.VITE_API_URL

Update your .env files:

## Change from:
REACT_APP_API_URL=https://api.example.com

## To:
VITE_API_URL=https://api.example.com

Use find-and-replace across your entire project to catch all references. Check configuration files, utility modules, and anywhere you access environment variables. You'll miss some and they'll bite you later.

Step 7: Fix CSS Modules

If you're using CSS modules, you need to rename files. Vite requires explicit .module.css file extensions:

// Webpack format (will break):
import styles from './Button.css'

// Vite format:
import styles from './Button.module.css'

Rename all CSS module files to include .module.css extension and update imports accordingly.

Step 8: Test Development Server

Start the development server to see what breaks:

npm run dev

When things break (and they will):

• Browser console for "Failed to resolve module specifier" errors
• Network tab in dev tools for 404 responses on assets
• Environment variables are accessible (console.log(import.meta.env))
• CSS imports load correctly without 404 errors
• Hot reload actually works (spoiler: it won't)

Reset option when debugging gets stuck:

rm -rf node_modules package-lock.json .vite
npm install
npm run dev

Step 9: Verify Production Build

Test production builds to catch issues that only appear in production:

npm run build
npm run preview

Production-only bullshit:

• Environment variables that work in development but are undefined in production (because of course they are)
• Different chunk splitting causing "Loading chunk 2 failed" errors that only happen in prod
• Asset path problems where /assets/logo.svg becomes /undefined/logo.svg somehow
• Source maps that point to the wrong files for no logical reason

Yeah, test production builds early and often.

Once you get the basic migration working (if you're lucky), you'll need to optimize for production and deal with team complaints about why everything takes forever now.

Bundle Size Optimization

Vite's default chunking strategy creates many small files instead of a few large bundles. You can control this if it annoys you:

export default defineConfig({
  build: {
    rollupOptions: {
      output: {
        manualChunks(id) {
          if (id.includes('node_modules')) {
            return 'vendor' // Combine all vendor dependencies
          }
        }
      }
    }
  }
})

Build performance optimization:

build: {
  minify: 'esbuild', // Faster minification than terser
  reportCompressedSize: false, // Skip size analysis for faster builds
}

Only optimize chunking if you identify actual performance issues. Don't prematurely optimize unless bundle sizes are actually causing problems (or your performance team is breathing down your neck).

Team Development Configuration

Fix common team issues by standardizing the development setup:

export default defineConfig({
  optimizeDeps: {
    include: [
      'react', 'react-dom', // Pre-bundle heavy dependencies
      'your-main-ui-library'
    ]
  },
  
  resolve: {
    alias: {
      '@': path.resolve(__dirname, 'src'), // Maintain consistent path aliases
    }
  }
})

API proxy configuration:

server: {
  proxy: {
    '/api': 'http://localhost:8080' // Backend server proxy
  }
}

This proxy config handles most common development scenarios where your frontend and backend run on different ports. Without it, you'll get CORS errors and spend an hour wondering what the fuck happened.

Production Debugging Tools

Bundle size analysis for when your bundles get too big:

// Install rollup-plugin-visualizer
import { visualizer } from 'rollup-plugin-visualizer'

plugins: [
  visualizer({ filename: 'dist/stats.html' })
]

Source map configuration for production debugging:

build: {
  sourcemap: true // Enable for easier production debugging
}

Source maps help when debugging production issues that only happen in prod.

Development Memory Management

Vite serves unbundled files during development, which uses more memory than webpack:

optimizeDeps: {
  include: ['heavy-dependencies'] // Pre-bundle large libraries
}

Pre-bundling heavy dependencies helps if memory becomes an issue.

Long-term Maintenance

Keep Vite updated: They release bug fixes frequently:

npm update vite @vitejs/plugin-react

Don't over-optimize: Start with basic configuration and only optimize when you identify actual performance problems.

You're done when dev server startup is fast and production deployments work. The migration itself is usually more annoying than difficult, but at least you'll never have to wait 45 seconds for webpack to start again.