//获取画布canvas的dom对象

          let canvas=document.createElement("canvas");
          let draw=canvas.getContext('2d');

         //时刻度  长
          for(var i=0;i< 12;i++){ 
             draw.save();
             draw.lineWidth=4;
             draw.strokeStyle="white" ;
             draw.translate(250,250);
             draw.rotate(i*30*Math.PI/180);
             draw.beginPath();
             draw.moveTo(0,170);
             draw.lineTo(0,190);
             draw.closePath();
             draw.stroke();
             draw.restore();
          }
          //分刻度  短
          for(let i=0;i< 60;i++){ 
              draw.save();
              draw.translate(250,250);
              draw.rotate(i*6*Math.PI/180);
              draw.lineWidth=2;
              draw.strokeStyle="white";
              draw.beginPath();
              draw.moveTo(0,190);
              draw.lineTo(0,180);
              draw.closePath();
              draw.stroke();
              draw.restore();
          }