SVG实现多彩圆环倒计时效果的示例代码分析

svg {
  transform: rotate(-0.05deg);
}
circle {
  transition: stroke-dasharray .2s;
}
.time-count-x {
  line-height: 1.5;
  position: relative;
}
.time-second {
  position: absolute;
  top: 50%; left: 0; right: 0;
  margin-top: -.75em;
  text-align: center;
  font-size: 100px;
}

<div id="timeCountX" class="time-count-x">
  <svg width="440" height="440" viewBox="0 0 440 440" class="center">
    <defs>
      <linearGradient x1="1" y1="0" x2="0" y2="0" id="gradient1">
        <stop offset="0%" stop-color="#e52c5c"></stop>
        <stop offset="100%" stop-color="#ab5aea"></stop>
      </linearGradient>
      <linearGradient x1="1" y1="0" x2="0" y2="0" id="gradient2">
        <stop offset="0%" stop-color="#4352f3"></stop>
        <stop offset="100%" stop-color="#ab5aea"></stop>
      </linearGradient>
    </defs>
    <g transform="matrix(0,-1,1,0,0,440)">
      <circle cx="220" cy="220" r="170" stroke-width="50" stroke="#f0f1f5" fill="none" stroke-dasharray="1069 1069"></circle>
      <circle cx="220" cy="220" r="170" stroke-width="50" stroke="url('#gradient1')" fill="none" stroke-dasharray="1069 1069"></circle>
      <circle cx="220" cy="220" r="170" stroke-width="50" stroke="url('#gradient2')" fill="none" stroke-dasharray="534.5 1069"></circle>
    </g>
  </svg>
  <span id="timeSecond" class="time-second"></span>
</div>

var eleCircles=document.querySelectorAll("#timeCountX circle");
var eleTimeSec=document.getElementById("timeSecond");
var perimeter=Math.PI*2*170;
var circleInit=function(){
  if(eleCircles[1]){
    eleCircles[1].setAttribute("stroke-dasharray","1069 1069")
  }
  if(eleCircles[2]){
    eleCircles[2].setAttribute("stroke-dasharray",perimeter/2+" 1069")
  }
  eleTimeSec.innerHTML=""
};
var timerTimeCount=null;
var fnTimeCount=function(b){
  if(timerTimeCount){
    return
  }
  var b=b||10;
  var a=function(){
    var c=b/10;
    if(eleCircles[1]){
      eleCircles[1].setAttribute("stroke-dasharray",perimeter*c+" 1069")
    }
    if(eleCircles[2]&&b<=5){
      eleCircles[2].setAttribute("stroke-dasharray",perimeter*c+" 1069")
    }
    if(eleTimeSec){
      eleTimeSec.innerHTML=b
    }
    b--;
    if(b<0){
      clearInterval(timerTimeCount);
      timerTimeCount=null;
      alert("时间到！");
      circleInit()
    }
  };
  a();
  timerTimeCount=setInterval(a,1000)
};
fnTimeCount();