Why is Safari confused about Date.getDay() for DST

问题:

Safari on OSX believes that October 6th, 2013 is a Saturday in Australia. It's not, it's actually a Sunday.

To replicate this issue, just set your time zone to Sydney-Australia, pop open the dev console in Safari, and enter new Date("2013/10/06"). You'll get this:

Now change to Seattle-US and you'll get this:

The problem also occurs for Melbourne-Australia but not for cities further north such as Brisbane (which fits the zoning for Australian DST), or a handful of other cities I've tested throughout the world.

Now, it just so happens that October 6th, 2013 is the start of daylight savings time in Sydney.. And the same mistake is made for the other DST start dates in other years. There does not seem to be a problem for DST end dates. There does not seem to be a problem for DST start dates in PDT time zone. Also, Chrome and Firefox do not exhibit this problem.

I've tested most of this on two different Macs, one on Snow Leopard with Safari 5.1.7 and one on Lion with Safari 6.0.2.

So the question is -- is this a bug or is there some kind of rational reason for this?

回答1:

This really should be considered a bug - Technically speaking DST in Sydney starts on 2013/10/06 at 2AM, so 2AM then becomes 3AM (http://www.timeanddate.com/worldclock/clockchange.html?n=240). It appears Safari in this case is thinking you mean 2013/10/06 at midnight - and is then going back 1 hour to 11PM the previous day. This doesn't even make sense because at 2AM the clock is supposed to go forward an hour.

I would recommend filing a bug report for this - because the output is so obviously wrong

https://developer.apple.com/bugreporter/