You can use objects and other things as keys for a Set or Map. As far as I know you can't do that for objects.

    const s = new Set();

    const a = {}, b = {};

    s.add(a);

    s.has(a); // true

    s.has(b); // false


    const o = {};

    o[a] = true;

    o[a]; // true

    o[b]; // true, cause its cast to a string like "[object Object]"

I've also seen Map perform faster than using an object as a Map.