JavaScript turns Date object into string to realize function

Converting Date object to string to implement function

function formatDate(time, format = "Y-MM-dd HH:mm:ss") {
  /**
    Format character description
    Y 	 Four digit year 2021
    The last two examples of Y year number 21
    M 	 The number of monthly units does not make up 0 example 1
    MM 	 Example 01 of supplement 0 for monthly unit number
    d 	 Example 2 of not adding 0 to the number of units per day
    dd 	 Example 02 of making up 0 for daily single digit
    H 	 24-hour system, unit number does not make up 0 example 3
    HH 	 24-hour system, unit number complements 0.03
    h 	 12 hour system, unit number does not make up 0 example 3
    hh 	 12 hour system, unit number makes up 0.03
    m 	 The unit number of minutes does not make up 0 example 4
    mm 	 Example 04 of making up 0 in minutes
    s 	 second 	 Unit number does not make up 0 example 5
    ss 	 second 	 Unit number complements 0 example 05 
  */
    
  let date = new Date(time);

  let yearFull = date.getFullYear().toString();
  let yearTwoDigits = yearFull.substr(2, 2);
  let month = date.getMonth() + 1; // The month starts at 0, so add 1
  let day = date.getDate();
  let hour = date.getHours(); //  24-hour system
  let hourTwelve = hour % 12; //  12 hour system
  let min = date.getMinutes();
  let sec = date.getSeconds();
  let preArr = Array.apply(null, Array(10)).map(function(elem, index) {
    return "0" + index;
  }); //  Create an array with a length of 10, and the format is 00 01 02 03, which is used to fill 0 for month, hour, minute, etc

  let newTime = format
    .replace(/Y/g, yearFull)
    .replace(/y/g, yearTwoDigits)
    .replace(/MM/g, preArr[month] || month)
    .replace(/M/g, month)
    .replace(/dd/g, preArr[day] || day)
    .replace(/d/g, day)
    .replace(/HH/g, preArr[hour] || hour)
    .replace(/H/g, hour)
    .replace(/hh/g, preArr[hourTwelve] || hourTwelve)
    .replace(/h/g, hourTwelve)
    .replace(/mm/g, preArr[min] || min)
    .replace(/m/g, min)
    .replace(/ss/g, preArr[sec] || sec)
    .replace(/s/g, sec);
  return newTime; 
}

//Run the test
formatDate(new Date().getTime()); // 2021-02-05 10:53:42
Formatdate (New date(). Gettime(), "mm / DD / yyyy")// February 5, 2021
formatDate(new Date().getTime(), "y-MM-dd"); // 21-02-05

let str_datetime = "2021/02/05 09:05:05".replace(/-/g,"/");
formatDate(new Date(str_ Datetime). Gettime (), "today is Y / mm / DD H: M: s")// Today is 2021-02-05 09:05:05
formatDate(new Date(str_ Datetime). Gettime (), "today is Y / mm / DD HH: mm: SS")// Today is 2021-02-05 09:05:05