WeakSet

I believe there has been somewhat a misunderstanding here. WeakSet is not a React JS specific term, it's actually a built-in global object in JavaScript.

In JavaScript, a WeakSet is a special type of Set that does not prevent its elements, which are always objects, from being garbage-collected. That means if there are no other references to an object that is stored in a WeakSet, that object can be automatically removed from the WeakSet by the garbage collector.

Here's an example of how you might use a WeakSet:

```javascript
let weakSet = new WeakSet();
let obj = {};

// add an object to the set
weakSet.add(obj);

console.log(weakSet.has(obj)); // true

// the object can still be garbage collected because the weakset doesn't prevent it from being memory-collected
obj = null;

console.log(weakSet.has(obj)); // false, it's been garbage-collected and removed from the set
```

As you can see, once `obj` was set to `null`, there were no other references to the initial object we put in the WeakSet, so it got garbage-collected and automatically removed from the set. `weakSet.has(obj)` then returned `false`.

Again, this isn't specific to React JS, but it is a feature of JavaScript that you could use in a React JS application.