Get days of a month of a year.

getdaysofmonth.js

// Arguments are NOT 0-based.
function getDaysOfMonth(yearInt, monthInt){                                                                                                                                                                                                                                                               
  return new Date(yearInt, monthInt, 0).getDate();                                                                                                                                                                                                                                                            
}

// Days of month for February 2011
getDaysOfMonth(2011, 2);
// 28

// Days of month for February 2012
getDaysOfMonth(2012, 2);
// 29