getPrettyTimeDiff, pass start date and end date to get string showing diff in days, hours, minutes, seconds

prettyTimeDiff.js

function getPrettyTimeDiff(startDateTime, endDateTime) {
  // get total seconds between the times
  let delta = Math.abs(endDateTime - startDateTime) / 1000;

  // calculate (and subtract) whole days
  let days = Math.floor(delta / 86400);
  delta -= days * 86400;

  // calculate (and subtract) whole hours
  let hours = Math.floor(delta / 3600) % 24;
  delta -= hours * 3600;

  // calculate (and subtract) whole minutes
  let minutes = Math.floor(delta / 60) % 60;
  delta -= minutes * 60;

  // what's left is seconds
  let seconds = delta % 60;  // in theory the modulus is not required

  const timeDiffArr = [
    { type: 'Days', val: days },
    { type: 'Hours', val: hours },
    { type: 'Minutes', val: minutes },
    { type: 'Seconds', val: seconds },
  ];

  return timeDiffArr.reduce((final, time) => {
    if(time.val > 0) {
      final += `${time.type}: ${time.val} `;
    }

    return final;
  }, '').trim();
}