Hint
Set uses SameValueZero for uniqueness: 1 !== "1", NaN === NaN (special case), undefined and null are distinct values.
const set = new Set([1, '1', true, 1, NaN, NaN, null, undefined, null]);
console.log(set.size);
console.log([...set]);6 [1, '1', true, NaN, null, undefined]
Explanation: 1 (number) and "1" (string) are different values. 1 appears twice — deduplicated. NaN appears twice — Set treats NaN === NaN (unlike === operator), so deduplicated. null twice — deduplicated. Result: 1, "1", true, NaN, null, undefined = 6 items.
Key Insight: Set uses SameValueZero for uniqueness: 1 !== "1", NaN === NaN (special case), undefined and null are distinct values.