doc22940 / microbundle

📦 Zero-configuration bundler for tiny modules.

Microbundle

The zero-configuration bundler for tiny modules, powered by Rollup.

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✨ Features:

• One dependency to bundle your library using only a package.json
• Support for ESnext & async/await (via Bublé & async-to-promises)
• Produces tiny, optimized code for all inputs
• Supports multiple entry modules (cli.js + index.js, etc)
• Creates multiple output formats for each entry (CJS, UMD & ESM)
• 0 configuration TypeScript support
• Built-in Terser compression & gzipped bundle size tracking

🔧 Installation

Download

npm i -D microbundle

Set up your package.json

{
  "source": "src/foo.js",          // Your source file (same as 1st arg to microbundle)
  "main": "dist/foo.js",           // output path for CommonJS/Node
  "module": "dist/foo.module.js",  // output path for JS Modules
  "unpkg": "dist/foo.umd.js",      // optional, for unpkg.com
  "scripts": {
    "build": "microbundle",        // uses "source" and "main" as input and output paths by default
    "dev": "microbundle watch"
  }
}

New: Modern JS

Microbundle now has a new modern format (microbundle -f modern). Modern output still bundles and compresses your code, but it keeps useful syntax around that actually helps compression:

// Our source, "src/make-dom.js":
export default async function makeDom(tag, props, children) {
	const el = document.createElement(tag);
	el.append(...(await children));
	return Object.assign(el, props);
}

Microbundle compiles the above to this:

export default async (e, t, a) => {
	const n = document.createElement(e);
	return n.append(...(await a)), Object.assign(n, t);
};

This is enabled by default - all you have to do is add the field to your package.json. You might choose to ship modern JS using the "module" field:

{
  "main": "dist/foo.umd.js",              // legacy UMD bundle (for Node & CDN's)
  "module": "dist/foo.modern.module.js",  // modern ES2017 bundle
  "scripts": {
    "build": "microbundle src/foo.js -f modern,umd"
  }
}

📦 Usage

Microbundle includes two commands - build (the default) and watch. Neither require any options, but you can tailor things to suit your needs a bit if you like.

microbundle / microbundle build

Unless overridden via the command line, microbundle uses the source property in your package.json to locate the input file, and the main property for the output.

For UMD builds, microbundle will use a snake case version of the name field in your package.json as export name. This can be overridden either by providing an amdName key in your package.json or via the --name flag in the cli.

microbundle watch

Acts just like microbundle build, but watches your source files and rebuilds on any change.

Using with TypeScript

Just point the input to a .ts file through either the cli or the source key in your package.json and you’re done.

Using CSS Modules

By default any css file imported as .module.css, will be treated as a css-module. If you wish to treat all .css imports as a module, specify the cli flag --css-modules true. If you wish to disable all css-module behaviours set the flag to false.

The default scope name when css-modules is turned on will be, in watch mode _[name]__[local]__[hash:base64:5] and when you build _[hash:base64:5]. This can be overriden by specifying the flag, eg --css-modules "_something_[hash:base64:7]". Note: by setting this, it will be treated as a true, and thus, all .css imports will be scoped.

flag	import	is css module?
null	import './my-file.css';	❌
null	import './my-file.module.css';	✅
false	import './my-file.css';	❌
false	import './my-file.module.css';	❌
true	import './my-file.css';	✅
true	import './my-file.module.css';	✅

Specifying builds in package.json

You can specify output builds in a package.json as follows:

"main": "dist/foo.js",          // CJS bundle
"umd:main": "dist/foo.umd.js",  // UMD bundle
"module": "dist/foo.m.js",       // ES Modules bundle
"source": "src/foo.js",         // custom entry module (same as 1st arg to microbundle)
"types": "dist/foo.d.ts",       // TypeScript typings

Mangling Properties

To achieve the smallest possible bundle size, libraries often wish to rename internal object properties or class members to smaller names - transforming this._internalIdValue to this._i. Microbundle doesn't do this by default, however it can be enabled by createing a mangle.json file (or a "mangle" property in your package.json). Within that file, you can specify a regular expression pattern to control which properties should be mangled. For example: to mangle all property names beginning an underscore:

{
  "mangle": {
    "regex": "^_"
  }
}

It's also possible to configure repeatable short names for each mangled property, so that every build of your library has the same output. See the wiki for a complete guide to property mangling in Microbundle.

All CLI Options

Usage
	$ microbundle <command> [options]

Available Commands
	build    Build once and exit
	watch    Rebuilds on any change

For more info, run any command with the `--help` flag
	$ microbundle build --help
	$ microbundle watch --help

Options
	-v, --version    Displays current version
	-i, --entry      Entry module(s)
	-o, --output     Directory to place build files into
	-f, --format     Only build specified formats  (default modern,es,cjs,umd)
	-w, --watch      Rebuilds on any change  (default false)
	--target         Specify your target environment (node or web)  (default web)
	--external       Specify external dependencies, or 'none'
	--globals        Specify globals dependencies, or 'none'
	--define         Replace constants with hard-coded values
	--alias          Map imports to different modules
	--compress       Compress output using Terser
	--strict         Enforce undefined global context and add "use strict"
	--name           Specify name exposed in UMD builds
	--cwd            Use an alternative working directory  (default .)
	--sourcemap      Generate source map  (default true)
	--raw            Show raw byte size  (default false)
	--jsx            A custom JSX pragma like React.createElement (default: h)
	--tsconfig       Specify the path to a custom tsconfig.json
	--css-modules    Configures .css to be treated as modules (default: null)
	-h, --help       Displays this message

Examples
	$ microbundle build --globals react=React,jquery=$
	$ microbundle build --define API_KEY=1234
	$ microbundle build --alias react=preact
	$ microbundle watch --no-sourcemap # don't generate sourcemaps
	$ microbundle build --tsconfig tsconfig.build.json

🛣 Roadmap

Here's what's coming up for Microbundle:

• Multiple separate inputs->outputs
• TypeScript support
• Flowtype support

🔨 Built with Microbundle

• Preact Fast 3kB React alternative with the same modern API. Components & Virtual DOM.
• Stockroom Offload your store management to a worker easily.
• Microenvi Bundle, serve, and hot reload with one command.
• Theme UI Build consistent, themeable React apps based on constraint-based design principles.
• react-recomponent Reason-style reducer components for React using ES6 classes.
• brazilian-utils Utils library for specific Brazilian businesses.
• react-hooks-lib A set of reusable react hooks.
• mdx-deck-live-code A library for mdx-deck to do live React and JS coding directly in slides.
• react-router-ext An Extended react-router-dom with simple usage.
• routex.js A dynamic routing library for Next.js.
• hooked-form A lightweight form-management library for React.
• goober Less than 1KB css-in-js alternative with a familiar API.

🥂 License

MIT