date_extremes.js

var getBeginningDate = function(period, date){
	var date = (date === undefined ? new Date() : new Date(date));
	if (period) {
		period = period.toLowerCase();
		switch (period) {
			case 'year':
				date.setMonth(0);
			case 'quarter':
				if (date.getMonth() >= 9) {
					date.setMonth(9);
				} else if (date.getMonth() < 9 && date.getMonth() >= 6) {
					date.setMonth(6);
				} else if (date.getMonth() < 6 && date.getMonth() >= 3) {
					date.setMonth(3);
				} else {
					date.setMonth(0);
				}
			case 'month':
				date.setDate(1);
			case 'week':
				if (date.getDate() > 1) date.setDate(Math.max(0, date.getDate() - date.getDay()));
			case 'day':
				date.setHours(0);
				date.setMinutes(0);
				date.setSeconds(0);
				date.setMilliseconds(0);
		}
	} else {
		date = getBeginningDate('year');
	}
	return new Date(date.valueOf());
}

var getEndDate = function(period, date){
	var date = (date === undefined ? new Date() : new Date(date));
	if (period) {
		period = period.toLowerCase();
		switch (period) {
			case 'year':
				date.setMonth(11);
			case 'quarter':
				if (date.getMonth() >= 9) {
					date.setMonth(11);                  
				} else if (date.getMonth() < 9 && date.getMonth() >= 6) {
					date.setMonth(8);
				} else if (date.getMonth() < 6 && date.getMonth() >= 3) {
					date.setMonth(5);
				} else {
					date.setMonth(2);
				}
			case 'month':
				var month = date.getMonth(), year = date.getFullYear();
				if ([0, 2, 4, 6, 7, 9, 11].indexOf(month) ) {
					date.setDate(31);
				}
				else if (month === 1) {
					date.setDate((((year % 4 == 0) && ( (!(year % 100 == 0)) || (year % 400 == 0))) ? 29 : 28 ));
				}
				else {
					date.setDate(30);
				}
			case 'week':
				if (date.getDay() < 6) {
					var newdate = new Date(date);
					newdate.setDate(date.getDate() + 6 - date.getDay());
					if (newdate.getFullYear() <= date.getFullYear() || period == 'week') date = newdate;
				}
			case 'day':
				date.setHours(23);
				date.setMinutes(59);
				date.setSeconds(59);
				date.setMilliseconds(999);
		}
	} else {
		date = getEndDate('year');
	}
	return new Date(date.valueOf());
}