JavaScript结合HTML5 Canvas绘制实时时钟

<html>
 <head>
 <meta charset="UTF-8">
 <title></title>
 <script type="text/javascript" src="js/demo3.js" ></script>
 </head>
 <body>
 <canvas id = "canvas"></canvas>
 </body>
</html>

var canvas,context;
function draw(){//定义划时钟的方法
 var data = new Date();
 var hHoure = data.getHours();
 var mMin = data.getMinutes();
 var sSec = data.getSeconds();
 var hValue = (hHoure*30+mMin/2-90)*Math.PI/180; 
 var mValue = (mMin*6-90)*Math.PI/180;
 var sValue = (sSec*6 -90)*Math.PI/180;
 var x = 200,y = 200,r = 150;
 
 context.clearRect(0,0,canvas.width,canvas.height);
 context.moveTo(x,y);
 context.arc(x,y,r,0,6*Math.PI/180,false);
 //
 context.beginPath();
 context.lineWidth = 1;
 for(var i = 0;i<60;i++){
 context.moveTo(x,y);
 context.arc(x,y,r,6*i*Math.PI/180,6*(i+1)*Math.PI/180,false);
 }
 context.closePath();
 context.stroke();
 //
 context.beginPath();
 context.fillStyle = "white";
 context.moveTo(x,y);
 context.arc(x,y,r/1.1,-0,2*Math.PI,false);
 context.closePath();
 context.fill();
 // 
 context.beginPath();
 context.lineWidth = 3;
 for(var i = 0;i<12;i++){
 context.moveTo(x,y);
 context.arc(x,y,r,30*i*Math.PI/180,30*(i+1)*Math.PI,false);
 }
 context.closePath();
 context.stroke();
 //
 context.beginPath();
 context.fillStyle = "white";
 context.moveTo(x,y);
 context.arc(x,y,r/1.12,0,2*Math.PI,false);
 context.closePath();
 context.fill();
 
 context.beginPath();
 context.fillStyle = "black";
 context.moveTo(x,y);
 context.arc(x,y,r/30,0,2*Math.PI,false);
 context.fill(); 
 //
 context.beginPath();
 context.lineWidth = 5;
 context.moveTo(x,y);
 context.arc(x,y,r/2.5,hValue,hValue,false);
 context.stroke();
 //
 context.beginPath();
 context.lineWidth = 3;
 context.moveTo(x,y);
 context.arc(x,y,r/2,mValue,mValue,false);
 context.stroke(); 
 //
 context.beginPath();
 context.lineWidth = 2;
 context.moveTo(x,y);
 context.arc(x,y,r/1.6,sValue,sValue,false);
 context.stroke();
}
window.onload = function(){
 canvas = document.getElementById('canvas');
 context = canvas.getContext('2d');
 canvas.height = 500;
 canvas.width = 500;
 setInterval(draw,1000); 
 draw(); 
}