weakSet vs Set

The main differences to the Set object are:

• WeakSets are collections of objects and symbols only. They cannot contain arbitrary values of any type, as Sets can.

• The WeakSet is weak, meaning references to objects in a WeakSet are held weakly. If no other references to a value stored in the WeakSet exist, those values can be garbage collected.

  Note: This also means that there is no list of current values stored in the collection. WeakSets are not enumerable.

  Source: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakSet