install.js

const path = require('path')
const fs = require('fs')
const child_process = require('child_process')

const root = process.cwd()
npm_install_recursive(root)
// Since this script is intended to be run as a "preinstall" command,
// it will do `npm install` automatically inside the root folder in the end.
console.log(
	'==================================================================='
)
console.log(`Performing "npm install" inside root folder`)
console.log(
	'==================================================================='
)
npm_install(root)

// Recurses into a folder
function npm_install_recursive(folder) {
	const has_package_json = fs.existsSync(path.join(folder, 'package.json'))

	// Abort if there's no `package.json` in this folder and it's not a "packages" folder
	if (!has_package_json && path.basename(folder) !== 'packages') {
		return
	}

	// If there is `package.json` in this folder then perform `npm install`.
	//
	// Since this script is intended to be run as a "preinstall" command,
	// skip the root folder, because it will be `npm install`ed in the end.
	// Hence the `folder !== root` condition.
	//
	if (has_package_json && folder !== root) {
		console.log(
			'==================================================================='
		)
		console.log(
			`Performing "npm install" inside ${
				folder === root ? 'root folder' : './' + path.relative(root, folder)
			}`
		)
		console.log(
			'==================================================================='
		)

		npm_install(folder)
	}

	// Recurse into subfolders
	for (let subfolder of subfolders(folder)) {
		npm_install_recursive(subfolder)
	}
}

// Performs `npm install`
function npm_install(where) {
	child_process.execSync('npm install', {
		cwd: where,
		env: process.env,
		stdio: 'inherit',
	})
}

// Lists subfolders in a folder
function subfolders(folder) {
	return fs
		.readdirSync(folder)
		.filter(subfolder =>
			fs.statSync(path.join(folder, subfolder)).isDirectory()
		)
		.filter(subfolder => subfolder !== 'node_modules' && subfolder[0] !== '.')
		.map(subfolder => path.join(folder, subfolder))
}