How-to: https://developer.wordpress.org/block-editor/how-to-guides/javascript/js-build-setup/
Open folder in terminal and run
npm init
Edit CAPITAL_WORDS during the process with your info
package name: (imm-gutenberg-boilerplate) PACKAGE_NAME
version: (1.0.0) PACKAGE_VERSION
description: PACKAGE_DESCRIPTION
entry point: (index.js) build/index.js
test command:
git repository:
keywords:
author: AUTHORNAME,
license: (ISC) GPL-3.0-or-later
About to write to .../package.json:
{
"name": "YOUR_PACKAGE_NAME",
"version": "YOUR_PACKAGE_VERSION",
"description": "YOUR_PACKAGE_DESCRIPTION",
"main": "build/index.js",
"scripts": {
"test": "echo \"Error: no test specified\" && exit 1"
},
"author": "YOUR_AUTHOR_NAME",
"license": "GPL-3.0-or-later"
}
Is this OK? (yes) yes
The @wordpress/script package can compile your code using build just once, or you can use start to run a watcher in terminal. In order to use this scripts you have to edit the package.json file just generated
...
"scripts": {
"start": "wp-scripts start",
"build": "wp-scripts build"
},
...
To use the scripts just run npm run start for development mode, or npm run build for package build.
Now it's time to install necessary packages. Run
npm install --save-dev --save-exact @wordpress/scripts@27 @wordpress/i18n
Now you can start writing your code editing index.js in src folder