javascript Date functions milliseconds to time hours minutes seconds

function msToTime(duration) {
  var milliseconds = parseInt((duration % 1000) / 100),
    seconds = Math.floor((duration / 1000) % 60),
    minutes = Math.floor((duration / (1000 * 60)) % 60),
    hours = Math.floor((duration / (1000 * 60 * 60)) % 24);

  hours = (hours < 10) ? "0" + hours : hours;
  minutes = (minutes < 10) ? "0" + minutes : minutes;
  seconds = (seconds < 10) ? "0" + seconds : seconds;

  return hours + ":" + minutes + ":" + seconds + "." + milliseconds;
}
// console.log(msToTime(300000))
// output: 00:05:00.0

// get time difference between two dates in seconds 
var startDate = new Date();
// Do your operations
var endDate   = new Date();
var seconds = (endDate.getTime() - startDate.getTime()) / 1000;
var milliseconds = (endDate.getTime() - startDate.getTime());

[, OPTIONAL second param [, OPTIONAL ... param]]
static Date.now() // returns the number of milliseconds elapsed since January 1, 1970 00:00:00 UTC.
parse(dateVal) //  Date.parse('05 Dec 1998 00:12:00 GMT'); // return 912816720000
toDateString() // sunday 19.7.2020
toTimeString() // 20:15:37
getDate() // 1-31
getDay() // 0-6, 0 == Sunday
var now = new Date();
var dayOfWeekSundayIs7 = now.getDay() == 0)?7:now.getDay();
getFullYear() // 2020
getHours() // 0-23
getMilliseconds() // eg. 956
getMinutes() //  0-59
getMonth() // 0 january 
getSeconds() // 0-59
getTime() // https://en.wikipedia.org/wiki/Unix_time
getTimezoneOffset() //returns the time zone difference, in minutes, from current locale 
getYear() //does not return full years ("year 2000 problem"), it is no longer used and has been replaced by the getFullYear() method.
setDate(numDate) // 1-31 day of month
setHours(numHours[, numMin[, numSec[, numMilli]]]) // now.setHours(20, 21, 22); 20:21:22
setMilliseconds(numMilli) // 0-999
setMinutes(numMinutes[, numSeconds[, numMilli]]) // 0-59, 0-59, 0-999
setMonth(numMonth[, dateVal]) // 0-11
setSeconds(numSeconds[, numMilli]) 0-59 [, 0-999]
setYear(numYear) // not set full years ("year 2000 problem"), it is no longer used and has been replaced by the setFullYear() method.
setUTCDate() // 
setUTCFullYear(2020) // 2020 sets the full year for a specified date according to universal time GMT
setUTCHours()
setUTCMilliseconds()
setUTCMinutes()
setUTCMonth()
setUTCSeconds()

toLocaleTimeString()
var options = { weekday: 'long', year: 'numeric', month: 'long', day: 'numeric' };
now.toLocaleDateString(undefined, options); //neděle 19. července 2020

// PDT Pacific Daylight Time (UTC -7)
// GMT ... SET GMT TIME +- ZONE ... new Date('December 31, 1974 23:59:30 GMT-3:00');
toGMTString() // DEPRECATED!!!! use toUTCString()
// Using UTC instead GMT!!!
var d = new Date("2020-07-15T00:00:00.000+07:00"); // UTC + 7
console.log(d.toISOString());  // "2020-07-14T17:00:00.000Z"
console.log(d.valueOf());      // 1594746000000

toISOString() // "2020-07-14T17:00:00.000Z"
toJSON() // "2020-07-14T17:00:00.000Z"
toSource() //This feature is obsolete!!!! Dont use!!!!
toString() // "Tue Jul 14 2020 19:00:00 GMT+0200 (Středoevropský letní čas)"
toUTCString() // "Tue, 14 Jul 2020 17:00:00 GMT"
valueOf() // 1594746000000