javascript - GMT vs UTC dates

Question

I have a calendar built in JavaScript that compares dates with PHP. The JavaScript date object is set using PHP, but, when I compare future dates, they appear to be out of sync.

PHP is set to GMT and JavaScript is set to UTC; how do these standards differ, and could this be causing the problem?

Answer 1

From Coordinated Universal Time on Wikipedia:

Coordinated Universal Time (UTC) is a time standard based on International Atomic Time (TAI) with leap seconds added at irregular intervals to compensate for the Earth's slowing rotation.

From Greenwich Mean Time on Wikipedia:

UTC is an atomic time scale which only approximates GMT with a tolerance of 0.9 second