The fifteenth of February isn't found

Question

I'm in javascript, running this in the console

d = new Date();    
d.setMonth(1);
d.setFullYear(2009);
d.setDate(15);          
d.toString();

outputs this:

"Sun Mar 15 2009 18:05:46 GMT-0400 (EDT)"

Why would this be happening? It seems like a browser bug.

Answer 1

d = new Date();
d.setDate(15);                    
d.setMonth(1);
d.setFullYear(2009);                                                                 
d.toString();

This works.

Answer 2

That's because when you initialize a new Date, it comes with today's date, so today is Oct 30 2008, then you set the month to February, so there is no February 30, so set first the day, then the month, and then the year:

d = new Date();
d.setDate(15);                    
d.setMonth(1);
d.setFullYear(2009);

But as @Jason W, says it's better to use the Date constructor:

new Date(year, month, date [, hour, minute, second, millisecond ]);

Answer 3

It's probably best to construct a Date object in one step to avoid the Date object being in an ambiguous or invalid state:

d = new Date(2009, 1, 15);

Answer 4

After a bunch of testing in FF3 on XP with Firebug, here are the things I can tell you

• Calling Date.setDate() after calling Date.setMonth() will generate this odd behavior.
• Date.setMonth() forces the timezone to be CST (or, some non DST-aware zone)
• Date.setDate() forces the timezone to be CDT (or, some DST-aware zone)

So, there's definitely something wonky going on with setMonth() and setDate() in respect to the timezone.

The only solution I can offer is this: Set the date before you set the month.