通过函数计算任意日期所在月和周的起始时间

//初始化一个时间date=2016-12-13,通过函数计算所在月和周的起始时间
function month(y,m,d){
var now = new Date(y,m-1,d);
var year = now.getFullYear();
var month = now.getMonth()+1;
var date = now.getDate();
var result;
if(month == 2){
if(year%400 == 0 || (year%4 == 0 && year%100 != 0)){
result =29;

}else{
result =28;
}
}else{
switch (month){
case 4:
case 6:
case 8:
case 9:
case 11:
result = 30;
break;
default:
result = 31;
break;
}
}
return "本月开始日期是" + year + "-" + month + "-01,结束日期是" + year + "-" + month + "-" +result;
}
var x = month(2017,2,13);
console.log(x);

function week(y,m,d){
var now = new Date(y,m-1,d);
var day = now.getDay();
if(day==0){
day = 7;
}
var time = now.getTime();
var startTime = time - (day-1)*24*60*60*1000;
var endTime = time + (7 - day)*24*60*60*1000;
var start = new Date(startTime).toLocaleDateString().split("/");
var end = new Date(endTime).toLocaleDateString().split("/");
if(start[1]<10){
start[1] = "0"+start[1];
}
if(start[2]<10){
start[2] = "0"+start[2];
}
if(end[1]<10){
end[1] = "0"+end[1];
}
if(end[2]<10){
end[2] = "0"+end[2];
}

console.log("本周开始的日期"+start[0]+"-"+start[1]+"-"+start[2]+",结束日期"+end[0]+"-"+end[1]+"-"+end[2]);
}
week(2016,2,5);