Creating increment limit

Question

Ok so I am making a like/dislike system for my website and I got it to work. The only problem is, is that a user can like something more than once, how do I stop this? heres my function

    function thumbup(uid, s) {
        const prevthumbs = s.thumbs

            firebase.db.collection('users').doc(uid).update({
                thumbs: prevthumbs + 1
            })
            
    }

How can I limit the increment to only one?

Answer 1

To limit how often the user can do something, use their UID as the key for the operation.

For example, if you don't have too many users, you can have a field likedBy in the document which is an array of the UIDs of the users who liked this user.

It's a bit unclear how to exactly implement it in your code for me, as you're already writing to a doc(uid), where usually the user is liking a post or something like that.