So much this. Not to mention that even within the same language, the implementation can differ (e.g. Firefox vs Chrome). I recently had to parse a bunch of dat

So much this. Not to mention that even within the same language, the implementation can differ (e.g. Firefox vs Chrome). I recently had to parse a bunch of dates in python, writing them to postgres, and then handle the same dates in javascript. And boy was it a PITA. The worst problem was the handling of "BC" dates. I had to hack my way around the boundary between python and sql. Javascript is no better, it simply doesn't compute BC dates without heavy hackery.