note that isNaN() will remain as it is today, coercing to a number (and so isNaN('LOL') will continue to return true). Number.isNaN() will have the new behavior

note that isNaN() will remain as it is today, coercing to a number (and so isNaN('LOL') will continue to return true). Number.isNaN() will have the new behavior, testing for actual IEEE 754 NaN values (and so returning false for Number.isNaN('LOL')). Such is the unfortunate price of backwards compatibility.