javascript - Time calculation with milliseconds in JS

Question

I want to find difference between two time with milliseconds value in Javascript. As you can see below snapshot, where I calculated two time values in Excel. My expectation exactly same calculated value with JS code. I tried some code snippet but I got slightly difference in seconds.

var d1 = '2020-12-15 01:00:23.788';
var d2 = '2020-12-15 01:00:55.482';
var date1 = new Date(d1);
var date2 = new Date(d2);
//date2 += 500;
//date2 = new Date(date2);
//date2.setMilliseconds(5);
var date1_ms = date1.getTime();
var date2_ms = date2.getTime();
// Calculate the difference in milliseconds
var difference_ms = date2_ms - date1_ms;
//take out milliseconds
difference_ms = difference_ms / 1000;
var seconds = Math.floor(difference_ms % 60);
difference_ms = difference_ms / 60;
var minutes = Math.floor(difference_ms % 60);
difference_ms = difference_ms / 60;
var hours = Math.floor(difference_ms % 24);

var demo = hours + ' hours, ' + minutes + ' minutes, and ' + seconds + ' seconds.' + difference_ms;
document.getElementById("demo").innerHTML = demo;

<h2>JavaScript new Date()</h2>

<p>new Date() creates a new date object with the current date and time:</p>

<p id="demo"></p>

Answer 1

JS does the same when correctly implemented

I tried with more interesting times

// Excel: 02:10:55,482 - 01:09:23,788 = 01:01:31,694

const fmtTime = date => {
  const hours = `0${date.getHours() - 1}`.slice(-2);
  const minutes = `0${date.getMinutes()}`.slice(-2);
  const seconds = `0${date.getSeconds()}`.slice(-2);
  const ms = `00${date.getMilliseconds()}`.slice(-3);
  return `${hours}:${minutes}:${seconds}.${ms}`
}


const from = "01:09:23,788"
const to = "02:10:55.482"
const re = /(d{2}):(d{2}):(d{2}).(d{3})/;
const [m1, fromhh, frommm, fromss, fromms] = from.match(re);
const [m2, tohh, tomm, toss, tomms] = to.match(re);

// method one

let d = new Date()
d.setHours(fromhh, frommm, fromss, fromms)
const fromTime = d.getTime()
d.setHours(tohh, tomm, toss, tomms)
const toTime = d.getTime()
const diffInMS1 = toTime - fromTime
console.log(diffInMS1)

d = new Date(diffInMS1);
console.log(fmtTime(d))


// Method 2 - Note I need to cast to int where I only add (+fromms)
let fromMS = (fromhh * 60 * 60 * 1000) + (frommm * 60 * 1000) + (fromss * 1000) + +fromms;
let toMS = (tohh * 60 * 60 * 1000) + (tomm * 60 * 1000) + (toss * 1000) + +tomms;
const diffInMS2 = toMS - fromMS;
console.log(diffInMS2)


d = new Date(diffInMS2);
console.log(fmtTime(d))