it’s loading all the super-efficient library.min.js Versions but you need to debug a JavaScript file?

open wp-config.php in your favourite editor an add: (right after define(‚WP_DEBUG‘, true);)

/**
 * For developers: WordPress debugging mode.
 *
 * Change this to true to enable the display of notices during development.
 * It is strongly recommended that plugin and theme developers use WP_DEBUG
 * in their development environments.
 */

define('WP_DEBUG', true);
define('SCRIPT_DEBUG', true); // Add define('SCRIPT_DEBUG', true); to wp-config.php to enable loading of non-minified,

in theory this should have some effect on functions like:

http://wordpress.org/wp-content/plugins/woocommerce/includes/class-wc-frontend-scripts.php

that are responsible for embedding the *.js woocommerce javascript libraries:

    /**
     * Register/queue frontend scripts.
     */

    public static function load_scripts() {
        global $post;

        $suffix               = defined( 'SCRIPT_DEBUG' ) && SCRIPT_DEBUG ? '' : '.min';
        $lightbox_en          = 'yes' === get_option( 'woocommerce_enable_lightbox' );
        $ajax_cart_en         = 'yes' === get_option( 'woocommerce_enable_ajax_add_to_cart' );
        $assets_path          = str_replace( array( 'http:', 'https:' ), '', WC()->plugin_url() ) . '/assets/';
        $frontend_script_path = $assets_path . 'js/frontend/';

        // Chosen is @deprecated as of 2.3 in favour of 2.3. Here for backwards compatibility.
        self::register_script( 'chosen', $assets_path . 'js/chosen/chosen.jquery' . $suffix . '.js', array( 'jquery' ), '1.0.0' );
        self::register_script( 'select2', $assets_path . 'js/select2/select2' . $suffix . '.js', array( 'jquery' ), '3.5.2' );

        // Register any scripts for later use, or used as dependencies
        self::register_script( 'jquery-blockui', $assets_path . 'js/jquery-blockui/jquery.blockUI' . $suffix . '.js', array( 'jquery' ), '2.70' );
        self::register_script( 'jquery-payment', $assets_path . 'js/jquery-payment/jquery.payment' . $suffix . '.js', array( 'jquery' ), '1.2.4' );
        self::register_script( 'jquery-cookie', $assets_path . 'js/jquery-cookie/jquery.cookie' . $suffix . '.js', array( 'jquery' ), '1.4.1' );
        self::register_script( 'wc-credit-card-form', $frontend_script_path . 'credit-card-form' . $suffix . '.js', array( 'jquery', 'jquery-payment' ) );
        self::register_script( 'wc-add-to-cart-variation', $frontend_script_path . 'add-to-cart-variation' . $suffix . '.js' );
        self::register_script( 'wc-single-product', $frontend_script_path . 'single-product' . $suffix . '.js' );
        self::register_script( 'wc-country-select', $frontend_script_path . 'country-select' . $suffix . '.js' );
        self::register_script( 'wc-address-i18n', $frontend_script_path . 'address-i18n' . $suffix . '.js' );

        // Register frontend scripts conditionally
        if ( $ajax_cart_en ) {
            self::enqueue_script( 'wc-add-to-cart', $frontend_script_path . 'add-to-cart' . $suffix . '.js' );
...

this way i was able to debug that:

https://wordpress.org/wp-content/plugins/woocommerce/assets/js/frontend/checkout.js

-> validate_field: function() {

is handling registration form input validation.

but if you have Plugin-Germanized installed: this one probably as well:

https://wordpress.org/wp-content/plugins/woocommerce-germanized/assets/js/revocation.min.js
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