simple-timer.js

/**
 * Creates a timer 
 * @param {number} secondsAmount Amount of time in seconds
 * @param {number} minutesAmount Amount of time in minutes
 * @param {number} hoursAmount Amount of time in hours
 * @param {number} daysAmount Amount of time in days
 * @returns an object representing the timer.
 */
function createTimer(
  secondsAmount = 0,
  minutesAmount = 0,
  hoursAmount = 0,
  daysAmount = 0,
) {
  if (daysAmount <= 0 && hoursAmount <= 0 && minutesAmount <= 0 && secondsAmount <= 0) {
    throw new RangeError('cannot define a timer without a proper time range')
  }

  if (daysAmount === 0 && hoursAmount === 0 && minutesAmount === 0 && secondsAmount === 0) {
    throw new Error('cannot define a timer without a proper start time')
  }

  let timerValue = 0
  timerValue += secondsAmount
  timerValue += (minutesAmount * 60)
  timerValue += (hoursAmount * 60 * 60)
  timerValue += (daysAmount * 24 * 60 * 60)
  const startTime = timerValue

  let timerInterval = setInterval(timeTick, 1000)

  const timerObj = {
    value: formatTimer(),
    continueTimer,
    pauseTimer
  }

  /**
   * Returns the formatted timer in `xx:xx:xx:xx`.
   * the format can be different based on the initial values.
   * @returns {string}
   */
  function formatTimer() {
    const days = Math.floor((timerValue / 24 / 60 / 60)).toString().padStart(2, '0')
    const hours = Math.floor((timerValue / 60 / 60) % 24).toString().padStart(2, '0')
    const minutes = Math.floor((timerValue / 60) % 60).toString().padStart(2, '0')
    const seconds = Math.floor(timerValue % 60).toString().padStart(2, '0')

    const timerArray = []

    if (startTime >= 86400) timerArray.push(days)
    if (startTime >= 3600) timerArray.push(hours)
    if (startTime >= 60) timerArray.push(minutes)
    timerArray.push(seconds)

    return timerArray.join(':')
  }

  /** triggers the timer to continue */
  function continueTimer() {
    if (timerInterval !== -1) return

    timerInterval = setInterval(timeTick, 1000)
  }

  /** triggers the timer to pause */
  function pauseTimer() {
    if (timerInterval === -1) return
    clearInterval(timerInterval)
    timerInterval = -1
  }

  function timeTick() {
    if (timerValue === 0) return

    timerValue -= 1
    timerObj.value = formatTimer()
  }

  return timerObj
}