Magento – Add to wishlist using ajax

One way to do this would be to create your own controller and action that will take the same information add to the wishlist but simply return a json response with success or a failure message.

In this way you can skip all the redirect stuff and work with a simply ajax action.

Don't want to advertise anything but Tigren ajax compare and wishlist module has fulfilled our requirements. Oh and also it is free and includes ajax add to cart and customer login functions too.

https://www.tigren.com/magento-2-extensions/ajax-suite-magento-2/