年月日

function yearToDay(time) {
  var y = time.getFullYear(),
  m = time.getMonth() + 1,
  d = time.getDate();
  m = m < 10 ? "0" + m : m;
  d = d < 10 ? "0" + d : d;
  return y + "-" + m + "-" + d;
};
//2022-03-31

年月日时分秒

function yearToSecond(time) {
  var h = time.getHours(),
  i = time.getMinutes(),
  s = time.getSeconds(),
  h = h < 10 ? "0" + h : h;
  i = i < 10 ? "0" + i : i;
  s = s < 10 ? "0" + s : s;
  return yearToDay(time) + ' ' + h + ':' + i + ':' + s;
};
//2022-03-31 10:15:20

年月日,时分秒补0

function yearToZero(){
  return yearToDay(time)+ " 00:00:00"
}
//2022-03-31 00:00:00

当前时间的前一天,后一天

let curDate = new Date()
var preDate = new Date(curDate.getTime() - 24*60*60*1000); //前一天
var nextDate = new Date(curDate.getTime() + 24*60*60*1000);//后一天
console.log(yearToSecond(preDate))//前一天
console.log(yearToSecond(nextDate))//后一天
//2022-03-30 10:15:20
//2022-04-01 10:15:20

当前月份第一天和最后一天

function getCurDay(){
  let nowdays = new Date(),
  year = nowdays.getFullYear(),
  month = nowdays.getMonth() + 1;
  month = month > 9 ? month : "0" + month;
  let firstDayOfCurMonth = `${year}-${month}-01`,
  lastDay = new Date(year, month, 0),
  lastDayOfCurMonth = `${year}-${month}-${lastDay.getDate()}`;
  return [firstDayOfCurMonth,lastDayOfCurMonth]
};
//['2022-03-01','2022-03-31']

当前月份上个月第一天和最后一天

function getPreDay() {
  let nowdays = new Date(),
  year = nowdays.getFullYear(),
  month = nowdays.getMonth();
  if (month == 0) {
    month = 12;
    year = year - 1;
  }
  month = month > 9 ? month : "0" + month;
  let firstDayOfPreMonth = `${year}-${month}-01`,
  lastDay = new Date(year, month, 0),
  lastDayOfPreMonth = `${year}-${month}-${lastDay.getDate()}`
  return [firstDayOfPreMonth,lastDayOfPreMonth]
};
//['2022-02-01', '2022-02-28']

当前时间最近三个月

function  getLast3Month() {
  var now = new Date(),
  year = now.getFullYear(),
  month = now.getMonth() + 1,
  day = now.getDate(),
  dateObj = {};
  month = month > 9 ? month : "0" + month;
  day = day > 9 ? day : "0" + day;
  dateObj.now = year + '-' + month + '-' + day;
  if (parseInt(month) == 1) {//如果是1月份，则取上一年的10月份
    dateObj.last = (parseInt(year) - 1) + '-10-' + day;
    return dateObj;
  }
  if (parseInt(month) == 2) {//如果是2月份，则取上一年的11月份
    dateObj.last = (parseInt(year) - 1) + '-11-' + day;
    return dateObj;
  }
  if (parseInt(month) == 3) {//如果是3月份，则取上一年的12月份
    dateObj.last = (parseInt(year) - 1) + '-12-' + day;
    return dateObj;
  }
  var preSize = new Date(year, parseInt(month) - 3, 0).getDate();//开始时间所在月的总天数
  if (preSize < parseInt(day)) {
    // 开始时间所在月的总天数<本月总天数，比如当前是5月30日，在2月中没有30，则取下个月的第一天(3月1日)为开始时间
    let resultMonth = parseInt(month) - 2 < 10 ? ('0' + parseInt(month) - 2) : (parseInt(month) - 2);  
    dateObj.last = year + '-' + resultMonth + '-01';  
    return dateObj;
  }
  if (parseInt(month) <= 10) {
    dateObj.last = year + '-0' + (parseInt(month) - 3) + '-' + day;
    return dateObj;
  } else {
    dateObj.last = year + '-' + (parseInt(month) - 3) + '-' + day;
    return dateObj;
  }
};
//{last: "2021-12-31",now: "2022-03-31" }

没了，结束了，是不是很简单呐，如有问题，欢迎留言。
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