Add Custom Fields to WooCommerce Registration

Add-Custom-Fields-to-WooCommerce-Registration.php

add_action( 'woocommerce_register_form', 'wc_extra_registation_fields' );
function wc_extra_registation_fields() {
    ?>
        <p class="form-row form-row-first">
            <label for="reg_role"><?php _e( 'Privat or commercial?', 'woocommerce' ); ?></label>
            <select class="input-text" name="role" id="reg_role">
            <option <?php if ( ! empty( $_POST['role'] ) && $_POST['role'] == 'customer') esc_attr_e( 'selected' ); ?> value="customer">private</option>
            <option <?php if ( ! empty( $_POST['role'] ) && $_POST['role'] == 'reseller') esc_attr_e( 'selected' ); ?> value="reseller">commercial</option>
            </select>
        </p>
    <?php
}

// Validate WooCommerce registration form custom fields.
add_action( 'woocommerce_register_post', 'wc_validate_reg_form_fields', 10, 3 );
function wc_validate_reg_form_fields($username, $email, $validation_errors) {
    if (isset($_POST['role']) && empty($_POST['role']) ) {
        $validation_errors->add('role_error', __('Role required!', 'woocommerce'));
    }
    return $validation_errors;
}