datum in javascript

function getBoundaries(dObj, dayFirst, dayLast) 
{
	var bounds = new Array();
	bounds[0] = new Date(dObj.getFullYear(), dObj.getMonth(), (dObj.getDate() + dayFirst));
	bounds[1] = new Date(dObj.getFullYear(), dObj.getMonth(), (dObj.getDate() + dayLast));
	return bounds;
}
	
function getWeekBoundaries(today) 
{
	var day = today.getDay();
	var startday = 1; // 0 = Sunday 1 = Monday
        var bounds;
	switch (day)
	{
		case 0:
			bounds = (startday) ? getBoundaries(today, 7, 0) : getBoundaries(today, 0, 6);
		break;
		case 1:
			bounds = (startday) ? getBoundaries(today, 0, 6) : getBoundaries(today, -1, 5);
		break;
		case 2:
			bounds = (startday) ? getBoundaries(today, -1, 5) : getBoundaries(today, -2, 4);
		break;
		case 3:
			bounds = (startday) ? getBoundaries(today, -2, 4) : getBoundaries(today, -3, 3);
		break;
		case 4:
			bounds = (startday) ? getBoundaries(today, -3, 3) : getBoundaries(today, -4, 2);
		break;
		case 5:
			bounds = (startday) ? getBoundaries(today, -4, 2) : getBoundaries(today, -5, 1);
		break;
		case 6:
			bounds = (startday) ? getBoundaries(today, -5, 1) : getBoundaries(today, 7, 0);
		break;
	}
	return bounds;
}
Date.prototype.getWeek = function()
{
	var thisDate = this;
	var year = thisDate.getFullYear();
	var month = thisDate.getMonth();
	var day = thisDate.getDate();

    month += 1; 

    var a = Math.floor((14-(month))/12);
    var y = year+4800-a;
    var m = (month)+(12*a)-3;
    var jd = day + Math.floor(((153*m)+2)/5) + 
                 (365*y) + Math.floor(y/4) - Math.floor(y/100) + 
                 Math.floor(y/400) - 32045;

    var d4 = (jd+31741-(jd%7))%146097%36524%1461;
    var L = Math.floor(d4/1460);
    var d1 = ((d4-L)%365)+L;
    NumberOfWeek = Math.floor(d1/7) + 1;
    return NumberOfWeek;        
}