How to add quantity to product archives in WooCommerce (and keep ajax)

Out of the box WooCommerce displays an Add to Cart button on product archive pages, but does not have the quantity input. There are a few solutions out there to achieve this, but none maintain ajax functionality (which is very handy on archive pages). Thankfully it’s super easy to get this up and running.

First, drop the following code to your functions.php file (remembering to remove the opening <?php tag), and WooCommerce will print out a nice quantity input box next to your add_to_cart button.