Build tool to generate proxy directories with package.json files such as this:

{
  "name": "redux-saga/effects",
  "private": true,
  "main": "../lib/effects.js",
  "module": "../es/effects.js"
}

When it comes to "main" entry points of our libraries we have an easy way for supporting both CJS & ESM files with respectively "main" and "module" fields in package.json. This allows resolution algorithms to chose a file with the best format automatically. However if we have multiple files in a package and we want all of them to be importable we often suggest to users doing it like this:

import module from "package/lib/module";

There are problems with this approach:

• it is often encouraging people to import files authored in CJS format, which if produced with tools like babel has i.e. interop helper functions deoptimizing imported file size when comparing to the same file authored in ESM format. Also webpack just bails out on CJS files when trying to optimize your application size with techniques such as tree-shaking & scope hoisting (a.k.a module concatenation).
• it is exposing internal directory structure to the user. Why lib is in the requested path? If you ship both CJS & ESM directories to npm and if users would like to import appropriate file depending on the tool they are "forced" to remember this and switch between importing the same thing with paths like package/lib/module and package/es/module. This is a mental overhead that can be avoided.

This technique was also described by me in more details in this article.

cherry-pick [input-dir]

Create proxy directories

Commands:
  cherry-pick [input-dir]        Create proxy directories              [default]
  cherry-pick clean [input-dir]  Cleanup generated directories

Options:
  --help, -h     Show help                                             [boolean]
  --version, -v  Show version number                                   [boolean]
  --cjs-dir                                                     [default: "lib"]
  --esm-dir                                                      [default: "es"]
  --types-dir
  --cwd                                                           [default: "."]
  --input-dir                                                   [default: "src"]

cherry-pick clean [input-dir]

Cleanup generated directories

Options:
  --help, -h     Show help                                             [boolean]
  --version, -v  Show version number                                   [boolean]
  --cwd                                                           [default: "."]
  --input-dir                                                   [default: "src"]

cherry-pick exports a default method which creates proxy directories and clean which removes them. Both accepts the same options as corresponding CLI commands, only they are camelCased.

const { default: cherryPick, clean } = require("cherry-pick");

cherryPick({ inputDir: "source" })
  .then(cherryPicked =>
    console.log(`Created proxy directories: ${cherryPicked.join(", ")}`)
  )
  .then(() => clean({ inputDir: "source" }))
  .then(removed =>
    console.log(`Removed proxy directories: ${Removed.join(", ")}`)
  );