JS 关于时间日期的处理

//n:获取的前几天数
//获取当前日期的前几天
formatDateUtil(n) {
var n = n;
var d = new Date();
var year = d.getFullYear();
var mon = d.getMonth() + 1;
var day = d.getDate();
if (day <= n) {
if (mon > 1) {
mon = mon - 1;
} else {
year = year - 1;
mon = 12;
}
}
d.setDate(d.getDate() - n);
year = d.getFullYear();
mon = d.getMonth() + 1;
day = d.getDate();
let s = year + "-" + (mon < 10 ? ('0' + mon) : mon) + "-" + (day < 10 ? ('0' + day) : day);
return s;
}

/**

从当前日期算起，获取N个月前的日期，日期格式为yyyy-MM-dd
java实现
@param mon 月份
@return
*/
public static String getDateByMonth(Integer mon) {
Date date = new Date();
int year = Integer.parseInt(new SimpleDateFormat("yyyy").format(date));
int month = Integer.parseInt(new SimpleDateFormat("MM").format(date)) - mon;
int day = Integer.parseInt(new SimpleDateFormat("dd").format(date));
if (month == 0) {
year -= 1;
month = 12;
} else if (day > 28) {
if (month == 2) {
if (year % 400 == 0 || (year % 4 == 0 && year % 100 != 0)) {
day = 29;
} else {
day = 28;
}
} else if ((month == 4 || month == 6 || month == 9 || month == 11)
&& day == 31) {
day = 30;
}
}
String y = year + "";
String m = "";
String d = "";
if (month < 10) {
m = "00" + month;
} else {
m = month + "";
}
if (day < 10) {
d = "0" + day;
} else {
d = day + "";
}
return y + "-" + m + "-" + d;

/**

从当前日期算起，获取N天前的日期（当前日不算在内），日期格式为yyyy-MM-dd
@param daily 天数
@return
*/
public static String getDateByDay(Integer daily) {
Date date = new Date();
int year = Integer.parseInt(new SimpleDateFormat("yyyy").format(date));
int month = Integer.parseInt(new SimpleDateFormat("MM").format(date));
int day = Integer.parseInt(new SimpleDateFormat("dd").format(date)) - daily;
if (day < 1) {
month -= 1;
if (month == 0) {
year -= 1;
month = 12;
}
if (month == 4 || month == 6 || month == 9 || month == 11) {
day = 30 + day;
} else if (month == 1 || month == 3 || month == 5 || month == 7
|| month == 8 || month == 10 || month == 12) {
day = 31 + day;
} else if (month == 2) {
if (year % 400 == 0 || (year % 4 == 0 && year % 100 != 0)) {
day = 29 + day;
}
else {
day = 28 + day;
}
}

}
String y = year + "";
String m = "";
String d = "";
if (month < 10) {
m = "0" + month;
} else {
m = month + "";
}
if (day < 10) {
d = "0" + day;
} else {
d = day + "";
}
return y + "-" + m + "-" + d;
}

链接:https://www.cnblogs.com/linjiqin/archive/2011/12/05/2276467.html