calculate time between inactive tab and active

function getTimeDiff(start, end) {
  const milliSecs = end - start

  const secs = Math.floor(milliSecs / 1000)
  const mins = Math.floor(secs / 60)
  
  const secsInMin = secs % 60
  const milliSecsInSec = milliSecs - (secs * 1000)

  return `${mins} mins ${secsInMin} secs ${milliSecsInSec} milliseconds`
}