Change Default Country Option on Checkout Page in Magento 2 – How to Guide

I solved.

The problem was actually that by default, the country was US instead of ES. On the checkout form, the dropdown selects Spain but it's not saved yet.

For solving this, I had to change Tax configuration, and set default country spain.

Create a custom component by extending Magento_Ui/js/form/element/abstract. Vendor_Module/view/frontend/web/js/custom-component.js:

define([
    'Magento_Ui/js/form/element/abstract'
], function (Component) {
    'use strict';

    return Component.extend({
        defaults: {
            imports: {
                update: 'checkout.steps.shipping-step.shippingAddress.shipping-address-fieldset.country_id:value'
            }
        },

        update: function (value) {
            this.visible(value !== 'NL');
        }
    });
});

This will result in the update function executing every time the value of the selected country changes. The new value is passed as a parameter.

Now use this component in your js layout instead of abstract:

'component' => 'Vendor_Module/js/custom-component'