Automatically selects the only available 'Variation Button' for Product Variations Swatches for WooCommerce.

product-variations-swatches-for-woocommerce-functions.php

function enqueue_script()
{
    $version = '1.0.0';
    if (is_product()) {
        wp_enqueue_script('single-variation-form', get_stylesheet_directory_uri() . '/js/single-variation-form.js', ['jquery', 'vi-wpvs-frontend-script'], $version, true);
    }
}

add_action('wp_enqueue_scripts', 'enqueue_script');

single-variation-form.js

(function($) {
	'use strict';

	function autoSelectSingleVariations() {
		$('.variations_form .vi-wpvs-variation-wrap').each(function() {
			const wrapper = $(this);
			const availableItems = wrapper.find('.vi-wpvs-option-wrap:not(.vi-wpvs-option-wrap-disable):not(.vi-wpvs-hidden)');
			const selectedItems = availableItems.filter('.vi-wpvs-option-wrap-selected');

			if (availableItems.length === 1 && !availableItems.attr('data-prevent-auto-select')) {
				availableItems.click();
			} else if (selectedItems.length > 0 && !selectedItems.attr('data-prevent-auto-select')) {
				selectedItems.click();
			}
		});
	}

	$(document).ready(function() {
		let clickedVariation = false;
		$('.vi-wpvs-option-wrap-selected').attr('data-prevent-auto-select', 'true');

		$('.variations_form').on('woocommerce_variation_has_changed', function() {
			setTimeout(function() {
				if (clickedVariation) {
					autoSelectSingleVariations();
				}
			}, 500);
		});

		$('.variations_form').on('click', '.reset_variations', function() {
			clickedVariation = false;
			$('.vi-wpvs-option-wrap').removeAttr('data-prevent-auto-select');
		});

		$('.vi-wpvs-option-wrap').on('click', function() {
			const button = $(this);
			if (button.attr('data-prevent-auto-select') && !button.hasClass('vi-wpvs-option-wrap-selected')) {
				clickedVariation = false;
				button.removeAttr('data-prevent-auto-select');
			} else {
				clickedVariation = true;
				button.attr('data-prevent-auto-select', 'true');
				button.closest('.vi-wpvs-variation-wrap').find('.vi-wpvs-option-wrap').not(this).removeAttr('data-prevent-auto-select');
			}
		});
	});

})(jQuery);