JS gets the instance code of the current time (yesterday, today, tomorrow)

  function getDay(day){
    var today = new Date()
    // Get the timestamp (millisecond level)    /*
       Day is 1, then tomorrow's time stamp
       Day is -1, which is yesterday's time stamp
       Day is -2, then the time stamp of the day before yesterday
     */
    var targetday_milliseconds = () + 1000 * 60 * 60 * 24 * day
    // (Timestamp): Set the time of the current date    (targetday_milliseconds)
    ('today=', today) // today= Sun Mar 05 2023 16:14:56 GMT+0800 (China Standard Time)    var tYear = () // Year    var tMonth = () // moon    var tDate = () // day    tMonth = (tMonth + 1)
    tDate = (tDate)
    ('Return to year, month, day=', tYear + '-' + tMonth + '-' + tDate)
    return tYear + '-' + tMonth + '-' + tDate
  }
  function doHandleMonth(month) {
    var m = month
    if (().length == 1) {
      m = '0' + month
    }
    return m
  }

/*
   * @params date
   * @params type date prev/current/next Yesterday/Today/Tomorrow
   * @params fmt date splicing symbol
 */
function getDays(date, type, fmt) {
    let currentDate = new Date(date)
    let y = ()
    let m = () + 1
    let d = ()
    function dateFormat(date, fmt) {
        let y = new Date(date).getFullYear()
        let m = new Date(date).getMonth() + 1
        let d = new Date(date).getDate()
        return `${y}${fmt}${m}${fmt}${d}`
    }
    switch (type) {
        case "prev":
            if (d - 1 < 1) {
                if (m - 1 < 1) {
                    y = y - 1
                    m = 12
                } else {
                    m = m - 1
                }
                d = new Date(y, m, 0).getDate()
            } else {
                d = d - 1
            }
            break
        case "current":
            break
        case "next":
            if (d + 1 > new Date(y, m, 0).getDate()) {
                if (m + 1 > 12) {
                    y = y + 1
                    m = 1
                    d = 1
                } else {
                    m = m + 1
                    d = 1
                }
            } else {
                d = d + 1
            }
            break;
    default:
      break;
    }
    return dateFormat(new Date(`${y}-${m}-${d}`), fmt)
}
(getDays(new Date('2023-5-13'), "prev", "-"));
(getDays(new Date('2023-5-30'), "next", "-"));
(getDays(new Date('2023-5-31'), "next", "-"));

// Yesterday's time var day1 = new Date();
 (()-24*60*60*1000);
 var s1 = ()+"-" + (()+1) + "-" + ();
 //Today's time var day2 = new Date();
 (());
 var s2 = ()+"-" + (()+1) + "-" + ();
 //Tomorrow's time var day3 = new Date();
 (()+24*60*60*1000);
 var s3 = ()+"-" + (()+1) + "-" + ();
 //Splicing time function show(){
  var str = "" + s1 + "to" + s2;
  return str;
 }
 //Assign doubleDate $('#dateS').val(show());

function writeCurrentDate() {
   var now = new Date();
   var year = (); //Get year   var month = ();//Get Month   var date = ();//Get date   var day = ();//What week do you want   var hour = ();//Get hours   var minu = ();//Get minutes   var sec = ();//Get seconds   var MS = ();//Get milliseconds   var week;
   month = month + 1;
   if (month < 10) month = "0" + month;
   if (date < 10) date = "0" + date;
   if (hour < 10) hour = "0" + hour;
   if (minu < 10) minu = "0" + minu;
   if (sec < 10) sec = "0" + sec;
   if （MS < 100）MS = "0" + MS;
   var arr_week = new Array("Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday");
   week = arr_week[day];
   var time = "";
   time = year + "Year" + month + "moon" + date + "day" + " " + hour + ":" + minu + ":" + sec + " " + week;
   //The current date is assigned to the current date input box (jQuery easyUI)   $("#currentDate").html(time);
   //Set the execution interval time of the function that gets the current date, refreshing every 1000 milliseconds.   var timer = setTimeout("writeCurrentDate()", 1000);
  }

 // Yesterday's time var day1 = new Date();
 (() - 1);
 var s1 = ("yyyy-MM-dd");
 //Time of the day before yesterday var day2 = new Date();
 (() - 2);
 var s2 = ("yyyy-MM-dd");

/**
  *Extension of Date, convert Date into String in the specified format
  * Month (M), day (d), hour (h), minute (m), seconds (s), quarter (q) can be used with 1-2 placeholders.
  *Year (y) can use 1-4 placeholders, and milliseconds (S) can only use 1 placeholder (it is a 1-3 digit number)
  *example:
  *(new Date()).Format("yyyy-MM-dd hh:mm:") ==> 2006-07-02 08:09:04.423
  *(new Date()).Format("yyyy-M-d h:m:") ==> 2006-7-2 8:9:4.18
  */
  = function (fmt) {
  var o = {
   "M+": () + 1, //month   "d+": (), //day   "h+": (), //Hour   "m+": (), //point   "s+": (), //Second   "q+": ((() + 3) / 3), //Quarterly   "S": () //millisecond  };
  if (/(y+)/.test(fmt)) fmt = (RegExp.$1, (() + "").substr(4 - RegExp.$));
  for (var k in o)
   if (new RegExp("(" + k + ")").test(fmt)) fmt = (RegExp.$1, (RegExp.$ == 1) ? (o[k]) : (("00" + o[k]).substr(("" + o[k]).length)));
  return fmt;
 }

var d = new Date();
((), () - ());
(())