js Date functions

dateAdd.js

/*
 * copied from http://stackoverflow.com/a/1214753
 */
function dateAdd(date, interval, units) {
  var ret = new Date(date); //don't change original date
  switch(interval.toLowerCase()) {
    case 'year'   :  ret.setFullYear(ret.getFullYear() + units);  break;
    case 'quarter':  ret.setMonth(ret.getMonth() + 3*units);  break;
    case 'month'  :  ret.setMonth(ret.getMonth() + units);  break;
    case 'week'   :  ret.setDate(ret.getDate() + 7*units);  break;
    case 'day'    :  ret.setDate(ret.getDate() + units);  break;
    case 'hour'   :  ret.setTime(ret.getTime() + units*3600000);  break;
    case 'minute' :  ret.setTime(ret.getTime() + units*60000);  break;
    case 'second' :  ret.setTime(ret.getTime() + units*1000);  break;
    default       :  ret = undefined;  break;
  }
  return ret;
}