I'm trying to find the index of an object in an array.

        for (let i = 0; i < sitesDeTir.length; i++) {
            let affIndex = affectations.findIndex((aff) => aff.id_sdt === sitesDeTir[i].id);
            if (affIndex === -1) {
                // action
            } else {
                // action
            }
        }

When I use the Chrome debugger, I can see that sitesDeTir[i].id is equal to 371 (number). I've also digged in the array (called affectations) and I see that there is an object who have id_sdt to 371 (number) but I always receive -1.

What I'm a missing here? I'm sorry for the link, I don't have enough reputation to embed it in the post.