What does console.log([NaN].indexOf(NaN), [NaN].includes(… output?

Console output

Why

NaN is the only value not equal to itself: NaN === NaN is false. indexOf compares with strict equality, so it can never find NaN and returns -1. includes (added in ES2016) uses the SameValueZero algorithm, which treats NaN as matching NaN, so it correctly returns true.