wp_ajax_pewc_add_child_product_to_cart.php

<?php

function pewc_ajax_add_child_product_to_cart() {
    $result = WC()->cart->add_to_cart( intval( $_POST['product_id'] ), intval( $_POST['quantity'] ) );
    $result ? wp_send_json_success() : wp_send_json_error();
}
add_action('wp_ajax_pewc_add_child_product_to_cart', 'pewc_ajax_add_child_product_to_cart');
add_action('wp_ajax_nopriv_pewc_add_child_product_to_cart', 'pewc_ajax_add_child_product_to_cart');



add_action( "wp_footer", function() {   
?>
<script>

jQuery(document).ready(function($) {

	$('.pewc-column-wrapper.child-product-wrapper .pewc-add-button:not(.pewc-added)').off("click").text("<?php echo __('Add to cart', 'pewc') ?>");
	$('.pewc-column-wrapper.child-product-wrapper .pewc-add-button:not(.pewc-added)').parent()
		.find('.pewc-child-quantity-field').removeClass('pewc-child-quantity-field').attr('min', 1).val(1).css('width', '75px');
	$('.pewc-column-wrapper.child-product-wrapper .pewc-variable-child-select').off("change click");

	$('.pewc-column-wrapper.child-product-wrapper').on('click', function(e) {
		
		// only allow 'Add' button to select child product, allow quickview
		if ( ! $(e.target).hasClass('pewc-child-quantity-field') && ! $(e.target).hasClass('pewc-show-quickview') ) {
			e.preventDefault();
			e.stopPropagation();
			
			// reverse auto-selection when opening quickview
			if ( $(e.target).hasClass('pewc-column-form-field') ) {
				$checkbox_image_wrapper = $(e.target).closest('.pewc-checkbox-image-wrapper');
				if ( $checkbox_image_wrapper.hasClass('checked') ) {
					$checkbox_image_wrapper.find('.pewc-add-button.pewc-added').click();
				} else {
					$checkbox_image_wrapper.find('.pewc-add-button:not(.pewc-added)').click();
				}
			}
		}

		// quantity field - prevent form submission on enter key
		if ( $(e.target).hasClass('pewc-form-field') && $(e.target).parent().hasClass('pewc-quantity-wrapper') ) {
			$('form.cart').on('click keydown', $(e.target), function(event) {
				if ( event.key === 'Enter' ) {
					event.preventDefault();
					event.stopPropagation();
				}
    		});
		}
		
	});

	$('.pewc-column-wrapper.child-product-wrapper .pewc-add-button:not(.pewc-added)').on('click', function(e) {
		
		let $child_product_add_btn = $(this);
		
		let quantity = $(this).closest('.pewc-checkbox-image-wrapper').find('.pewc-quantity-wrapper input').val();
		if ( $(this).closest('.child-product-wrapper').hasClass('products-quantities-linked') ) {
			quantity = $(this).closest('form.cart').find('input.qty').val();
		} else if ( ! quantity ) {
			quantity = 1;
		}
		
		let product_id = $(this).closest('.pewc-checkbox-image-wrapper').find('.pewc-column-form-field').val();
		if ( $(this).closest('.pewc-checkbox-image-wrapper').hasClass('pewc-variable-child-product-wrapper') ) {
			product_id = $(this).closest('.pewc-checkbox-image-wrapper').find('.pewc-variable-child-select').val();
		}
		
		// prevent multiple clicks
		$child_product_add_btn.css('pointer-events', 'none');
		
		$.ajax({
      		url: pewc_vars.ajaxurl,
      		type: 'POST',
      		data: {
          		action: 'pewc_add_child_product_to_cart',
          		product_id: product_id,
          		quantity: quantity
      		},
			success: function( response ) {
				if ( response.success ) {
					$child_product_add_btn.css({
						"color": "#333333",
						"background-color": "#eeeeee",
						"border-color": "#eeeeee"
					}).text("<?php echo __('Added to cart', 'pewc') ?>");
					$child_product_add_btn.parent().find('input').prop('disabled', true); 
					$('body').trigger("wc_fragment_refresh");                
				} else {
					$child_product_add_btn.css('pointer-events', 'auto');
					console.log('Failed to add product to cart.');
				}
			}
		});
		
	});

});


</script>
<?php
}, 9999 );