I'm creating a simple button to add to cart (woocommerce) a specific number (quantity) of products without refreshing the page.

Using the following href link I can add 1 unit of my product to basket without refreshing:

<a href="?add-to-cart=3475" data-quantity="1" class="button product_type_simple add_to_cart_button ajax_add_to_cart" rel="nofollow">Add to cart</a>

How can I change the the 'data-quantity' value from some HTML input value defined by the user?

I tried several ways, and they just add one unit or add the updated units but forcing a refresh.