//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();
	  }