SOURCE

var hourspan =document.getElementById("hour");
  var minutespan =document.getElementById("minute");
  var secondspan =document.getElementById("second");
  var dom = document.getElementById("clock");
  var ctx = dom.getContext("2d");
  var width = ctx.canvas.width;
  var height = ctx.canvas.height;
  var r = width/2;
  

  function drawBackground(){
    ctx.save(); //保存当前画布样式
    ctx.translate(r,r);//切换中心点
//画外圆
    ctx.beginPath();
    ctx.lineWidth = 10;
    
    
    var grd = ctx.createLinearGradient(-120,-120,0,0);
    grd.addColorStop(0, "rgb(120,120,120)");
    grd.addColorStop(1, "rgb(30,30,30)");
    ctx.strokeStyle = grd;
    
    
    ctx.arc(0,0,r-8,0,2*Math.PI,false);
    ctx.stroke();
//画外圆投影
    ctx.beginPath();
    ctx.lineWidth = 16;
    
    
    var grd = ctx.createRadialGradient(0,0,r-24, 0,0,r+5);
    grd.addColorStop(0, "rgb(243,245,246)");
    grd.addColorStop(1, "rgb(150, 150, 150)");
    ctx.strokeStyle = grd;
    
    
    ctx.arc(0,0,r-20,0,2*Math.PI,false);
    ctx.stroke();
//画数字
    // var hourNumber = [3,4,5,6,7,8,9,10,11,12,1,2];
    // ctx.textAlign = "center";
    // ctx.textBaseline = "middle";
    // hourNumber.forEach(function(item,index){
    //   var rad = 2*Math.PI/12*index;
    //   var x = Math.cos(rad)*(r-30);
    //   var y = Math.sin(rad)*(r-30);
    //   ctx.fillText(item,x,y);
    // })
//画时刻
    for(var i=0;i<60;i++){
      var rad = 2*Math.PI/60*i;
      var x = Math.cos(rad)*(r-26);
      var y = Math.sin(rad)*(r-26);
      ctx.beginPath();
      ctx.arc(x,y,3,0,Math.PI*2,false);
      if(i%5 == 0){
        ctx.fillStyle = "#ddd";
        ctx.fill();
      }
      // else{
      //   ctx.fillStyle = "#ccc";
      //   ctx.fill();
      // }
    }
  }
//画时针，分针，秒针
  function drawHour(hour,minute,second){
    ctx.save();
    ctx.beginPath();
    var rad = 2*Math.PI/12*hour+((2*Math.PI/12)*(minute+second/60)/60);//将分，秒换算成小时
    ctx.rotate(rad);
    ctx.strokeStyle = "#000";
    ctx.lineWidth = 8;
    ctx.lineCap = "round";
    ctx.moveTo(0,10);
    ctx.lineTo(0,-r/2);
    ctx.stroke();
    ctx.restore();//返回上一个画布样式
  }
  function drawMinute(minute,second){
    ctx.save();
    ctx.beginPath();
    var rad = 2*Math.PI/60*minute+(2*Math.PI/60)*(second/60);//将秒换算成分
    ctx.rotate(rad);
    ctx.strokeStyle = "#000";
    ctx.lineWidth = 5;
    ctx.lineCap = "round";
    ctx.moveTo(0,15);
    ctx.lineTo(0,-(r-40));
    ctx.stroke();
    ctx.restore();
  }
  function drawSecond(second){
    ctx.save();
    ctx.beginPath();
    ctx.strokeStyle = "rgb(200, 0, 0)";
    var rad = 2*Math.PI/60*second;
    ctx.rotate(rad);
    ctx.lineWidth = 2;
    ctx.lineCap = "round";
    ctx.moveTo(0,20);
    ctx.lineTo(0,-(r-25));
    ctx.stroke();
    ctx.restore();
  }
//画圆心
  function drawCicle(){
    ctx.save();
    ctx.beginPath();
    ctx.fillStyle ="#fff";
    ctx.arc(0,0,4,0,Math.PI*2,false);
    ctx.fill();
    ctx.restore();
  }
  
  
  //将所有事件封装在一个函数中，为制作成动态时钟做准备
  function timeActive(){
    ctx.clearRect(0,0,width,height);//清空整个画布
    var date = new Date();
    var hour = date.getHours();
    var minute = date.getMinutes();
    var second = date.getSeconds();
    hourspan.innerText = hour;
    minutespan.innerText = minute;
    secondspan.innerText = second;
    drawBackground();
    drawHour(hour,minute,second);
    drawMinute(minute,second);
    drawSecond(second);
    drawCicle();
    ctx.restore();
  }
  timeActive();//初始化画布
  setInterval(timeActive,1000);

<div class="box">
    <span id="hour"></span>:
    <span id="minute"></span>:
    <span id="second"></span>
  </div>
  <div>
<canvas id="clock" width="360px" height="360px"></canvas>

*{margin: 0;padding: 0;}
div{
  text-align: center;
}
div.box{
  margin: 50px auto;
  text-align: center;
  font-size: 30px;
  display: flex;
  align-items: center;
  justify-content: center;
}
span{
  display: inline-block;
  font-size: 20px;
  margin: 0px 20px;
}
canvas{
  transform: scale(.5)
}