trying to add plus minus to quantity selector but jquery is not working

Technical Q&A
1

here is my code:

in product-template.liquid


 

  
  

   -
   
   +

in qty.liquid which I include in theme.liquid

the style is working, but the jquery is not, what is wrong?

i modified the solution from here https://community.shopify.com/c/Shopify-Design/Add-Quantity-Buttons-to-Debut-Theme/td-p/593001

2

turn out I overlooked the “jQuery not defined” error in console, so I include the jQuery file myself

and the problem solved

still I don’t quite understand why I have to add the file again, because I am sure jQuery is already defined (I confirmed this by logging the console)