Until you start seeing times like 24:45 in your app. The spec has some really strange behaviour in it that defaults to "1-24"-hour time instead of the common "0-23" if you specify hour12: false.

Only Chrome seems to have actually implemented the spec this strictly, they don't want to change it: https://bugs.chromium.org/p/chromium/issues/detail?id=104579...

It isn't the pure javascript feeling without a few cross-browser quirks.