Luiz Paulo

function daysInMonth(month,year) {
	var m = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
	if (month != 2) return m[month - 1];
	if (year % 4 != 0) return m[1];
	if (year % 100 == 0 && year%400 != 0) return m[1];
 
	return m[1] + 1;
}

function daysInMonth(month,year) {
	var dd = new Date(year, month, 0);
	return dd.getDate();
}

var lastDay = (new Date(year, month, 0)).getDate();

function getLastDayOfMonth(month,year)
{
	var day;
 
	switch(month)
	{
		case 1 :
		case 3 :
		case 5 :
		case 7 :
		case 8 :
		case 10:
		case 12:
			day = 31;
			break;
		case 4 :
		case 6 :
		case 9 :
		case 11:
		   	day = 30;
			break;
		case 2 :
			if( ( (year % 4 == 0) && ( year % 100 != 0) ) || (year % 400 == 0) )
				day = 29;
			else
				day = 28;
			break;
 
	}
	return day;
}

function anoBissexto(anoCompleto) 
{
	if(!(anoCompleto%4) && (anoCompleto%100 || !(anoCompleto%400))) return true;
	return false;
}
function diasNoMes(mes,ano)
{
	var var_type=typeof mes;
	if(var_type != "number" && var_type != "string") return false;
	if(var_type == "number" && (mes > 11 || mes < 0) && !isInt(mes)) return false;
	var eng_args_allowed = "january-february-march-april-may-june-july-august-september-october-november-december";
	var bra_args_allowed = "janeiro-fevereiro-marçomarco-abril-maio-junho-julho-agosto-setembro-outubro-novembro-dezembro";
	var vet_eng_args_allowed = eng_args_allowed.split("-");
	var vet_bra_args_allowed = bra_args_allowed.split("-");
	var datahj = new Date();
	var anohj = datahj.getFullYear();
	var dias = [31,anoBissexto(ano)?29:28,31,30,31,30,31,31,30,31,30,31];
 
	if(var_type == "string")
	{
		indice_eng = keyPosMatch(vet_eng_args_allowed,mes);
		indice_bra = keyPosMatch(vet_bra_args_allowed,mes);
		if(indice_eng>=0) return dias[indice_eng];
		if(indice_bra>=0) return dias[indice_bra];
		return false;
	}
	else return dias[mes];
}