Change SKU's with Variant Change in theme with OS 1.0

Store Design
, ,
1

I have an old theme build on OS 1.0 and I am trying to display variants sku’s.

I have tried the solution given by shopify which is this:

<div class="sku">
        {% assign current_variant = product.selected_or_first_available_variant %}
         <span class="variant-sku">SKU: {{ current_variant.sku }}</span>
</div>

This only show the first variant when the product page loads. I asked the theme support and they say that I need to add ajax for the variant change.

Can some please help me with that AJAX/JS. Thank