htmelt

Experimental bundler for HTML, powered by ESBuild and LightningCSS. It "melts" (hence the name htmelt) any CSS and JS found in your HTML files into CSS/JS bundles.

_{You should probably just use Vite.}

Features

• custom plugins with the bundle.config.js file
• ESBuild integration (TypeScript + ESM syntax, code splitting, dynamic imports)
• LightningCSS integration
• Browserslist integration
• HTML entry point scanning
• JS/CSS bundling
• import.meta.glob support
• worker bundling with new URL('./worker.ts', import.meta.url)
• great for Web Extension development
  • dev server for painless extension reloading
  • run multiple browsers at once (or use --webext=chromium to only run Chrome)
• --watch mode
  • CSS hot reloading
  • HTML rebuild on JS/HTML changes
  • sets NODE_ENV=development
• default mode
  • HTML/JS/CSS minification
  • critical CSS extraction (via isCritical option or --critical flag)
  • sets NODE_ENV=production

Usage

Before running htmelt, you should move your HTML files into the src/ directory and use relative paths for JS/CSS references inside your HTML files.

# Run in development mode
pnpm htmelt --watch

# Run in production mode
pnpm htmelt

If you want TypeScript to recognize import.meta.glob calls, you can add the following to your tsconfig.json file.

{
  "compilerOptions": {
    "lib": ["esnext"],
    "types": ["htmelt/client.d.ts"]
  }
}

Configuration

The bundle.config.js file allows for customization.

export default {
  // Browserslist targets.
  targets: ['defaults', 'not IE 11'],
  // Input and output directories.
  src: './src',
  build: './build',
  // Tool-specific options.
  esbuild: {...},
  lightningcss: {...},
  // If true, will extract critical CSS from the HTML files.
  isCritical: false,
  // If true, will delete the build directory before building.
  deletePrev: false,
}