@metalsmith/js-bundle

A metalsmith plugin that bundles your JS using esbuild with sensible defaults (and babel for ES5)

Features

• Transpiles ESnext to ES6 with esbuild, and falls back on a Babel compatibility layer for ES5
• Supports most ESbuild options including custom loaders and plugins
• Available in CommonJS and ESM

Installation

NPM:

npm install @metalsmith/js-bundle

Yarn:

yarn add @metalsmith/js-bundle

Usage

Pass @metalsmith/js-bundle to metalsmith.use :

import jsBundle from '@metalsmith/js-bundle'

metalsmith.use(
  jsBundle({
    // defaults
    entries: {
      index: 'lib/index.js'
    }
  })
)

const isProd = metalsmith.env('NODE_ENV') !== 'development'
metalsmith.use(
  jsBundle({
    // explicit defaults
    bundle: true,
    minify: isProd,
    sourcemap: !isProd,
    platform: 'browser',
    target: 'es6',
    assetNames: '[dir]/[name]',
    // accessible as process.env.<NAME> in your JS files
    define: metalsmith.env(),
    // removes console & debugger statements
    drop: isProd ? ['console', 'debugger'] : [],
    entries: {
      index: 'lib/index.js'
    }
  })
)

The key of the entries option determines the location of the processed file. For example index: 'lib/index.js' will result in /index.js, while '/assets/index': 'lib/index.js' will result in `/assets/index.js'.

The paths in the entries option should be relative to metalsmith.directory().

Options

@metalsmith/js-bundle provides access to most underlying esbuild options, with a few notable differences:

The options absWorkingDir (=metalsmith.directory()), outdir (=metalsmith.destination()), write (=false), and metafile (=true) can not be set, they are determined by the plugin.

The option entryPoints is renamed to entries. Specify entries as a {'target': 'path/to/source.js' }} object, and mind that the target should not have an extension.

The option define is automatically filled with metalsmith.env(), but can be overwritten if desired. metalsmith.env('DEBUG') would be accessible in the bundle as process.env.DEBUG.

Loading assets

You can load assets with any of the ESbuild loaders by specifying a loader map. By default there is support for .js,.ts,.css,.json,.jsx,.tsx, and .txt loading. It's important to note 2 things:

• assets loaded with any loader but the file loader will be "embedded" in the resulting JS bundle and removed from the build (=not available for other plugins), increasing bundle size.
• if you would like to process assets loaded with the file loader with other metalsmith plugins (eg metalsmith-imagemin) @metalsmith/js-bundle needs to be run first and you should not overwrite the default assetNames option [dir]/[name].

The file loader is the loader you need for most large asset types you wouldn't want to bloat your JS bundle with. If you want to use inline SVG's, you would set its loader to text, while if you prefer loading them in image tags, you could set them to dataurl (embedded) or file (external).

The publicPath option will prepend a path to each asset loaded with the file loader. This can be useful if you are serving the metalsmith build from a non-root URI.

metalsmith.use(
  jsbundle({
    entries: { index: 'src/index.js' },
    loader: {
      '.png': 'file',
      '.svg': 'dataurl',
      '.jpg': 'file', // this will be a relative URI
      '.yaml': 'text' // this will be a parseable string
    },
    publicPath: metalsmith.env('NODE_ENV') === 'development' ? '' : 'https://johndoe.com'
  })
)

ES5 transpilation support

ESbuild does not support compiling to ES5 (ie. supporting IE 11 and some older mobile browsers). Nevertheless you can specify the target: 'es5' option and @metalsmith/js-bundle will let ESbuild handle bundling and fall back on Babel to provide a compatibility layer. The side effects of this are a slower and bigger build and currently, no support for source maps. However, you can make the target depend on an environment variable and enjoy sourcemaps in development, eg:

const isDev = process.env.NODE_ENV === 'development'

metalsmith.use(
  jsbundle({
    entries: { index: 'src/index.js' },
    target: isDev ? 'es6' : 'es5'
  })
)

At the moment, passing options to Babel is not supported. A Babel production build will have basic minification, but without further (mangling) optimizations. You could choose to use metalsmith-uglifyjs to further optimize it.

Alternatively you could run @metalsmith/jsbundle twice, 1 with target es5, and 1 with higher, and decide with an inline script at run-time which bundle to inject.

Debug

To enable debug logs, set metalsmith.env('DEBUG', '@metalsmith/js-bundle*') or in metalsmith.json: "env": { "DEBUG": "@metalsmith/js-bundle*" }. You can also pass the live environment variable by running metalsmith.env('DEBUG', process.env.DEBUG) or in metalsmith.json: "env": { "DEBUG": "$DEBUG" }

Alternatively you can set DEBUG to @metalsmith/* to debug all Metalsmith core plugins.

CLI usage

To use this plugin with the Metalsmith CLI, add @metalsmith/js-bundle to the plugins key in your metalsmith.json file:

{
  "plugins": [
    {
      "@metalsmith/js-bundle": {
        "entries": {
          "app": "lib/main.js"
        }
      }
    }
  ]
}

License

MIT