Change script depending, if the product is in stock and or not in stock

Hi guys,

I have a script for showing when product will be dispatched:

{{ ‘//cdnjs.cloudflare.com/ajax/libs/datejs/1.0/date.min.js’ | script_tag }}

It needs to be only shown, if product.description does not contain :

“BUY NOW TO PRE-ORDER!” words. As we have some products in stock and pre-order.

Can anyone help how to change this script properly?

Thanks