Change milliseconds to a timestamp in the format `HH:MM:SS`

milliseconds-to-timestamp.js

/**
 *
 * @param {number} milliseconds - time in milliseconds
 * @returns {string} - time in hours, minutes, seconds
 */
function millisecondsToTimestamp(milliseconds) {
  if(milliseconds < 0) {
    return '00:00:00';
  }
  if(milliseconds === 0) {
    return '00:00:00';
  }
  // 1- Convert to seconds:
  let seconds = milliseconds / 1000;
  // 2- Extract hours:
  const hours = Math.floor(seconds / 3600)
    .toString()
    .padStart(2, "0"); // 3,600 seconds in 1 hour
  seconds %= 3600; // seconds remaining after extracting hours
  // 3- Extract minutes:
  const minutes = Math.floor(seconds / 60)
    .toString()
    .padStart(2, "0"); // 60 seconds in 1 minute
  // 4- Keep only seconds not extracted to minutes:
  const secondsString = Math.floor(seconds % 60)
    .toString()
    .padStart(2, "0");
  // 5- Return formatted time:
  return `${hours}:${minutes}:${secondsString}`;
}
export default millisecondsToTimestamp;

milliseconds-to-timestamp.test.js

import { it, expect, describe } from 'vitest'

import millisecondsToTimestamp from "../src/common-utilities/milliseconds-to-timestamp";

describe('millisecondsToTimestamp', () => {
  it('should convert milliseconds to timestamp', () => {
    // easy peasy
    expect(millisecondsToTimestamp(1000)).toBe('00:00:01');
    expect(millisecondsToTimestamp(60000)).toBe('00:01:00');
    expect(millisecondsToTimestamp(3600000)).toBe('01:00:00');
    expect(millisecondsToTimestamp(3661000)).toBe('01:01:01');
  });
  it('should work for edge cases', ()=> {
    // Test when milliseconds is a minus number
    expect(millisecondsToTimestamp(-61000)).toBe('00:00:00');
    // Test when milliseconds is 0
    expect(millisecondsToTimestamp(0)).toBe('00:00:00');

    // Test when milliseconds is less than 1000 (less than a second)
    expect(millisecondsToTimestamp(500)).toBe('00:00:00');

    // Test when milliseconds is just over a minute
    expect(millisecondsToTimestamp(61000)).toBe('00:01:01');

    // Test when milliseconds is just over an hour
    expect(millisecondsToTimestamp(3661000)).toBe('01:01:01');

    // Test when milliseconds is just under a day
    expect(millisecondsToTimestamp(86399000)).toBe('23:59:59');

    // Test when milliseconds is exactly a day
    expect(millisecondsToTimestamp(86400000)).toBe('24:00:00');

    // Test when milliseconds is just over a day
    expect(millisecondsToTimestamp(86401000)).toBe('24:00:01');
  })
});