Timezone freakiness

Just solved a mind-boggling problem I was having with some date manipulation.

The Date constructor returns a date with a different timezone depending on whether the date is today & before, or in the future.

var today:Date = new Date();

var yesterday:Date = new Date( today.fullYear, today.month, today.date – 1 );

var today2:Date =    new Date( today.fullYear, today.month, today.date     );

var tomorrow:Date =  new Date( today.fullYear, today.month, today.date + 1 );

trace( yesterday.timezoneOffset );

trace( today2.timezoneOffset );

trace( tomorrow.timezoneOffset );

Traces output:

300

300

240

What’s worse if you then subtract a day from “tomorrow” it doesn’t equal today.

tomorrow.date–;

trace( tomorrow.time == today.time );

trace( tomorrow == today );

Output: false / false

Guess why?

Today’s daylight savings switchover day.  Arghhh.

I really wish Actionscript had a date-only type.