Floating point NaN is not equal to any number including itself. NaN == NaN is always false (even if the bits are same). NaN != NaN is always true. 1.0 / +0.0 == +Inf , 1.0 / -0.0 == -Inf )JS use floating point for all numbers. (Putting millisecond timestamp integer in JSON fine, as millisecond timestamp exceeds limit in year 287396.