Who the hell made the JS version? ECMA Standard does not distinguish between different kinds of NaN values, which means the JS version is abusing undefined behaviour. Whatever solution that passed the test will not work in general.

Also: https://esdiscuss.org/topic/how-many-nans-do-we-now-have

Edit:

Java NaN bit patterns are processor-dependent.

Python does not guaranteed that a signaling NaN survives a round-trip (which seems to be dependent on system, architecture and math library).

C11 standard does not differentiate between qNaN and sNaN either.