<script type="text/java script">
//开始之前必须懂得时针各指针的弧度计算公式。
var canvas,context;
function window_onload(){
canvas = document.getElementById("myCanvas");
context = canvas.getContext("2d");
setInterval("draw()",1000);
}
function draw(){
///得到当前系统时间的：时、分、秒
var now_date=new Date();
var radius = Math.min(canvas.width/2,canvas.height/2),
sec=now_date.getSeconds(),
min=now_date.getMinutes(),
hour=now_date.getHours();
hour=hour>=12 hour-12:hour;

//初始化画布
context.save();
context.clearRect(0,0,canvas.width,canvas.height);
context.translate(canvas.width/2,canvas.height/2);
context.scale(0.9,0.9);
context.rotate(-Math.PI/2);
context.save();

//小时刻度
context.strokeStyle="black";
context.fillStyle="black";
context.lineWidth=3;
context.lineCap="round";
context.beginPath();
for(var i=0;i<12;i++){
context.rotate(Math.PI/6);
context.moveTo(radius-30,0);
context.lineTo(radius-10,0);
}
context.stroke();
context.restore();
context.save();

//分钟刻度
context.lineWidth=2;
context.beginPath();
for(var i=0;i<60;i++){
if(i%5!=0){
context.moveTo(radius-15,0);
context.lineTo(radius-10,0);
}
context.rotate(Math.PI/30);
}
context.stroke();
context.restore();
context.save();

//画上时针
context.rotate((Math.PI/6)*hour+(Math.PI/360)*min+(Math.PI/21600)*sec);
context.lineWidth=6;
context.lineCap="butt";
context.beginPath();
context.moveTo(-10,0);
context.lineTo(radius*0.5,0);
context.stroke();
context.restore();
context.save();

//分针
context.rotate((Math.PI/30)*min+(Math.PI/1800)*sec);
context.strokeStyle="#29A8DE";
context.lineWidth=4;
context.lineCap="butt";
context.beginPath();
context.moveTo(-20,0);
context.lineTo(radius*0.7,0);
context.stroke();
context.restore();
context.save();

//秒针
context.rotate(sec*Math.PI/30);
context.strokeStyle="red";
context.lineWidth=2;
context.lineCap="butt";
context.beginPath();
context.moveTo(-30,0);
context.lineTo(radius*0.9,0);
context.stroke();
context.restore();
context.save();

///表框
context.lineWidth=4;
context.strokeStyle="gray";
context.beginPath();
context.arc(0,0,radius,0,Math.PI*2,true);
context.stroke();
context.restore();
context.restore();
}

效果图：