How Does Javascript Know The Time Zone Of A Date In Milliseconds?

The following code when executed using w3schools' interactive js environment (here): var d1=new Date(1306796400000); document.write('Original form: ' + d1); displays the following

Solution 1:

There is no special flag. It's just Daylight Savings in effect.

Solution 2:

Javascript is executed inside of the user's browser, which in turn, reads the current time zone from user's OS. That's how it can "guess" the proper time zone.

Solution 3:

The milliseconds do not contain any such flag. However, the time zone of the date object you create using new Date(n) is dependent upon the locale in your interpreter/browser. For me:

var d = newDate(1231977600000);

d.toString();
// "Wed Jan 14 2009 17:00:00 GMT-0700 (Mountain Standard Time)"

d.toUTCString();
// "Thu, 15 Jan 2009 00:00:00 GMT"

Solution 4:

It does not. It uses local timezone information, including DST transition date. Hence the difference in

javascript:alert([newDate(1306796400000),newDate(1231977600000)].join('\n'))

Set your locale to DST-less timezone and the difference will disappear.