Add to wishlist button on Category Page Opencart:2.3.0.2

Question

I want to add a wishlist icon on Category page, like on the Product page.

<a onclick="wishlist.add('<?php echo $product_id; ?>');"><i class="icon-heart"></i> </a>

But this did not work in Category page. I also checked for jquery in product page with keyword "wishlist", but didn't find at all. So, where does this even is handled? And how can I implement it on Category Page?

Answer 1

Yes, Solved.

When I change

$product_id;

to

$product['product_id'];

Then it has an ID(Like: wishlist.add(56) ).