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Creating binary files

A binary is an executable file distributed in an npm package via the bin field. Packemon offers first class support for binary files by:

  • Prepending a #!/usr/bin/env node shebang to the output file. Do not include this in the source file!
  • Updating the bin field in package.json to the output file (if not already defined).

To make use of this functionality, you must define an input with the name bin, like so.

"name": "package",
"packemon": {
"inputs": {
"bin": "src/bin.ts"
"platform": "node"

The contents of the binary source file can be whatever you want, but do be aware that code in the module scope will be executed immediately when the file is executed by Node.js.

Customizing Babel, swc, and Rollup

This is an advanced escape hatch and should be avoided unless absolutely necessary, for example, processing CSS files in a way that Packemon does not support.

Customizing the Babel, swc, and Rollup configs are an opt-in feature, and require the following conditions to be met:

  • A --loadConfigs option is passed on the command line. This enables searching and loading of config files, otherwise, we want to avoid the filesystem lookups.
  • A packemon.config.{ts,js} file at the monorepo/polyrepo root, which applies customizations to all packages. Or optional .packemon.{ts,js} files within each package, which applies customizations to that package individually. An example of this is found below, or view the @boost/config docs.
├── src/
├── package.json
├── packemon.config.js

Both of these config files have the same structure, and may define the fields below. All of these fields require a function (except swc), which is passed the finalized config as an argument (with output fields also accepting the current build as the 2nd argument). This config can then be mutated in place.

  • babelInput - For parsing syntax into an AST (TypeScript, JSX, etc).
  • babelOutput - For applying transformations.
  • rollupInput - For defining inputs, outputs, and more.
  • rollupOutput - For customizing each output.
  • swc - Enables swc instead of Babel.
  • swcInput - For parsing syntax into an AST (TypeScript, JSX, etc).
  • swcOutput - For applying transformations.
import type { ConfigFile } from 'packemon';
import linaria from '@linaria/rollup';

const config: ConfigFile = {
babelOutput(config, build) {
rollupInput(config) {

export default config;

We suggest not mutating the config that Packemon generates, as it may break our assumptions. Instead, prefer to only apply additions that add new functionality.

Stamping releases

For situations where you update Packemon and want to release every package, even those that have not been modified since the last release, you can use stamping. Stamping is a very simple concept where we modify the package.json of each package with a release timestamp, and can be achieved by passing --stamp to the build or pack commands.

Version constraints

If you're using packemon as a global dependency and want to ensure all contributors of your project are using the correct packemon version, you can provide an engines constraint to your root package.json.

"name": "package",
"engines": {
"packemon": "^1.0.0"