countdown.js

// Credit: Mateusz Rybczonec

const FULL_DASH_ARRAY = 283;
const WARNING_THRESHOLD = 10;
const ALERT_THRESHOLD = 5;

const COLOR_CODES = {
  info: {
    color: "green"
  },
  warning: {
    color: "orange",
    threshold: WARNING_THRESHOLD
  },
  alert: {
    color: "red",
    threshold: ALERT_THRESHOLD
  }
};

const TIME_LIMIT = 90;
let timePassed = 0;
let timeLeft = TIME_LIMIT;
let timerInterval = null;
let remainingPathColor = COLOR_CODES.info.color;

function onTimesUp() {
  clearInterval(timerInterval);
}

function startTimer() {
  timerInterval = setInterval(() => {
    timePassed = timePassed += 1;
    timeLeft = TIME_LIMIT - timePassed;
    document.getElementById("base-timer-label").innerHTML = formatTime(
      timeLeft
    );
    setCircleDasharray();
    setRemainingPathColor(timeLeft);

    if (timeLeft === 0) {
      onTimesUp();
      // Dispatch the event
      const elem = document.getElementById("timer");
      const event = new CustomEvent('timesUp');
      elem.dispatchEvent(event);
    }
  }, 1000);
}

function formatTime(time) {
  const minutes = Math.floor(time / 60);
  let seconds = time % 60;

  if (seconds < 10) {
    seconds = `0${seconds}`;
  }

  return `${minutes}:${seconds}`;
}

function setRemainingPathColor(timeLeft) {
  const { alert, warning, info } = COLOR_CODES;
  if (timeLeft <= alert.threshold) {
    document
      .getElementById("base-timer-path-remaining")
      .classList.remove(warning.color);
    document
      .getElementById("base-timer-path-remaining")
      .classList.add(alert.color);
  } else if (timeLeft <= warning.threshold) {
    document
      .getElementById("base-timer-path-remaining")
      .classList.remove(info.color);
    document
      .getElementById("base-timer-path-remaining")
      .classList.add(warning.color);
  }
}

function calculateTimeFraction() {
  const rawTimeFraction = timeLeft / TIME_LIMIT;
  return rawTimeFraction - (1 / TIME_LIMIT) * (1 - rawTimeFraction);
}

function setCircleDasharray() {
  const circleDasharray = `${(
    calculateTimeFraction() * FULL_DASH_ARRAY
  ).toFixed(0)} 283`;
  document
    .getElementById("base-timer-path-remaining")
    .setAttribute("stroke-dasharray", circleDasharray);
}