Retrieve the last day of the year in javascript

alert(new Date(2012, 12, 0));

will return

Mon Dec 31 00:00:00 CST 20102

In case that someday the last day of the year changes, could be useful to use a temporary date with the first day on the next month and then return to the previous date

tmp_date = new Date(2012, 12, 1)
last_day = new Date(tmp_date - 1)

Since the last day of a year is always December 31, it's easy:

new Date(new Date().getFullYear(), 11, 31)