How WooCommerce deals with frontend scripts
All the WooCommerce frontend scripts are located in the folder:
wp-content/plugins/woocommerce/assets/js/frontend
These scripts are loaded in the file
wp-content/plugins/woocommerce/includes/class-wc-frontend-scripts.php
How to override a specific frontend script in WooCommerce
Say for example you want to use your own frontend script for the checkout page.
Copy the checkout.js file from the folder above.
Paste it in a new folder, eg. themes/my-site/woocommerce/js/checkout.js
Make your custom modifications in the pasted file.
In your functions.php add the following code.
add_action('wp_enqueue_scripts', 'override_woo_frontend_scripts');
function override_woo_frontend_scripts() {
wp_deregister_script('wc-checkout');
wp_enqueue_script('wc-checkout', get_template_directory_uri() . '/woocommerce/js/checkout.js', array('jquery', 'woocommerce', 'wc-country-select', 'wc-address-i18n'), null, true);
}