Sort Objects by Date Property

Array.prototype.sortByDate = function(sortOrder) {
	var objArray = this;    // [Obj, Obj, Obj] where each Obj 
                                // has prop: "sortDate" with val: "YYYY-MM-DD"
 
	var sBD = function(a, b) {
		var dateStringA = a.sortDate.split("-");
		var dateStringB = b.sortDate.split("-");
		var dateA = new Date(dateStringA[0], dateStringA[1], dateStringA[2]);
		var dateB = new Date(dateStringB[0], dateStringB[1], dateStringB[2]);
		return dateA - dateB;
	};
 
	if (sortOrder == "desc") {
		objArray.sort(sBD).reverse();
	} else if (sortOrder == "asc") {
		objArray.sort(sBD);
	} else if (!sortOrder) {
		objArray.sort(sBD);
	}
}