{{ block title }} Page title {{ endblock }} {{ block content }}
<p> The time lefts <span id="countdowntimer">15 </span> Seconds</p>
<script type="text/javascript">
    var timeleft = 15;
    var downloadTimer = setInterval(function(){
    timeleft--;
    document.getElementById("countdowntimer").textContent = timeleft;
    if(timeleft <= 0)
        clearInterval(downloadTimer);
    },1000);
    
</script>
<div id="app">a</div>
<style>
    body {
  font-family: sans-serif;
  display: grid;
  height: 100vh;
  place-items: center;
}

.base-timer {
  position: relative;
  width: 300px;
  height: 300px;
}

.base-timer__svg {
  transform: scaleX(-1);
}

.base-timer__circle {
  fill: none;
  stroke: none;
}

.base-timer__path-elapsed {
  stroke-width: 7px;
  stroke: grey;
}

.base-timer__path-remaining {
  stroke-width: 7px;
  stroke-linecap: round;
  transform: rotate(90deg);
  transform-origin: center;
  transition: 1s linear all;
  fill-rule: nonzero;
  stroke: currentColor;
}

.base-timer__path-remaining.green {
  color: rgb(65, 184, 131);
}

.base-timer__path-remaining.orange {
  color: orange;
}

.base-timer__path-remaining.red {
  color: red;
}

.base-timer__label {
  position: absolute;
  width: 300px;
  height: 300px;
  top: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 48px;
}
</style>
<script>// 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 = 200;
    let timePassed = 0;
    let timeLeft = TIME_LIMIT;
    let timerInterval = null;
    let remainingPathColor = COLOR_CODES.info.color;
    
    document.getElementById("app").innerHTML = `
    <div class="base-timer">
      <svg class="base-timer__svg" viewBox="0 0 100 100" xmlns="http://www.w3.org/2000/svg">
        <g class="base-timer__circle">
          <circle class="base-timer__path-elapsed" cx="50" cy="50" r="45"></circle>
          <path
            id="base-timer-path-remaining"
            stroke-dasharray="283"
            class="base-timer__path-remaining ${remainingPathColor}"
            d="
              M 50, 50
              m -45, 0
              a 45,45 0 1,0 90,0
              a 45,45 0 1,0 -90,0
            "
          ></path>
        </g>
      </svg>
      <span id="base-timer-label" class="base-timer__label">${formatTime(
        timeLeft
      )}</span>
    </div>
    `;
    
    startTimer();
    
    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();
        }
      }, 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);
    }</script>
{{ endblock }}

<!--参考文献:https://pote-chil.com/js_timer/,
    https://css-tricks.com/how-to-create-an-animated-countdown-timer-with-html-css-and-javascript/!>