JavaScript Sets lost reference but don't change size

Question

I'm storing objects references inside my JavaScript Sets:

let set1 = new Set();

let obj  = {};

Then if I use the has() method and the size property of the Set objects I get the next results:

console.log(set1.size) //it returns 1

console.log(set1.has(obj)) //it returns true

But, if I remove the reference of the object using the next code:

obj = null;

Then strange behaviour happens to me:

console.log(set1.size); //it returns 1 because they are Hard Sets.

console.log(set1.has(obj)); //it returns false

In the last line, why does it return false if the size is not changed? Then the reference is lost but the size is not changed.

Answer 1

In the last line, why does it return false if the size is not changed?

It returns size = 1 because it still holds one value (a reference to that object).

It returns false because it does not has a value that is equals to null.

But, if I remove the reference of the object using the next code:

You just overwrite a value of the variable. After that there is still one reference to the object left (inside the Set).

To remove an element from a Set you need to use Set.prototype.delete() method:

set1.delete(obj);

Presumably you need to do that while obj still holds a reference to the object.

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