How should I call Set?

let a = new Set();

let b = new Set();

a.add(1);

a.add(2);

a.add(3);

b.add(a);

console.log(b); //Set(1) {Set(3)}

console.log(b.has(Set(3))); // error

Why? then, how can I call Set?

And I expected that

console.log(b.has({1,2,3})); // true