How to use composer to install libraries for the Webform module

For anybody facing the question of what is the best-recommended method for installing/updating/managing all libraries required by the Webform module, the answer is to install libraries using composer!

The Webform module comes shipped with a "composer.libraries.json" file containing information about all up-to-date libraries required by the module itself, and so we will be using this file to install all libraries by merging the "composer.libraries.json" with the "composer.json" file of our Drupal website.

1) Composer Merge plugin

The merging is accomplished by the aid of the Composer Merge Plugin plugin available on GitHub, so from the project directory, open a terminal and run:
composer require wikimedia/composer-merge-plugin

2) Merge the composer.libraries.json file

You have these two alternative options:

2.a) Using the file provided by the module

Edit the "composer.json" file of your website and under the "extra": { section add:

* note: the `web` represents the folder where drupal lives like: ex. `docroot`.

        "merge-plugin": {
            "include": [
                "web/modules/contrib/webform/composer.libraries.json"
            ]
        },

From now on, every time the "composer.json" file is updated, it will also read the content of "composer.libraries.json" file located at web/modules/contrib/webform/ and update accordingly.

2.b) Use drush to append webform libraries in a custom file

Generate a custom file according to options set in webform libraries config page running:

drush webform:libraries:composer > DRUPAL_ROOT/composer.libraries.json

Edit the "composer.json" file of your website and under the "extra": { section add:

        "merge-plugin": {
            "include": [
                "composer.libraries.json"
            ]
        },

From now on, every time the "composer.json" file is updated, it will also read the content of "composer.libraries.json" file and update accordingly. 

But in this case you need to update this file after dependencies updates or config changes in your webform libraries config page by running again:

drush webform:libraries:composer > DRUPAL_ROOT/composer.libraries.json

3) Install libraries

You have these two alternative options:

3.a) As a CDN

In order for the "composer.json" file to install all the libraries mentioned as a CDN inside the "composer.libraries.json", from a terminal, run composer update --lock .

This method will assure that all the libraries will be served from CDN and automatically updated once the "composer.libraries.json" is updated with new versions of the Webform module.

Notice that this update ALL your dependencies, not just the webform libraries. If you prefer just load the webform libraries, go for 3.b instead.

3.b) As local files

If you want to install all the mentioned libraries in a local directory on your webserver, typically web/libraries, then you need to run
composer update drupal/webform "drupal/webform-*" --with-dependencies

This method will ensure that composer will pull the libraries from the CDN source and store a copy in your libraries directory in your Drupal installation.