使用canvas绘制时钟

window.onload=function(){

    var clock=document.getElementById("clock").getContext('2d');//通过获取canvas元素获取2d上下文

    var width=clock.canvas.width;//得到画布的宽度

    var height=clock.canvas.height;//得到花布的高度

    var r=width/2;//得到将要画的时钟的半径

    var prop=width/150;//在此保留比例，以便于在更换画布大小时调节

    function outline(){

        clock.save();//保存当前状态

        clock.translate(r,r);//将原点移动到(r,r)处

        clock.beginPath();//每个函数内部都要有beginPath()方法

        clock.lineWidth=3*prop;//通过lineWidth来设置划线的宽度，注意这里没有单位

        clock.arc(0,0,r-clock.lineWidth/2,0,2*Math.PI,false);

        clock.stroke();//绘制路径

        var scaleNumbers=[3,4,5,6,7,8,9,10,11,12,1,2];

        clock.font=12*prop+"px Arial";//通过font来设置字体的大小。关键：一定单位px，且后面一定要有字体样式

        clock.textAlign="center";//设置位水平居中

        clock.textBaseline="middle";//设置位垂直居中

    <strong>    scaleNumbers.forEach(function(number,i){//遍历数组

            var rad=2*Math.PI/12*i;

            var x=Math.cos(rad)*(r-15*prop);

            var y=Math.sin(rad)*(r-15*prop);

            clock.fillText(number,x,y);//在x y处绘制number

        });</strong>

        for(var i=0;i<=60;i++){

            var rad=2*Math.PI/60*i;

            var x=Math.cos(rad)*(r-7*prop);

            var y=Math.sin(rad)*(r-7*prop);

            clock.beginPath();

            if(i%5===0){

                clock.fillStyle="red";//填充的颜色

                clock.arc(x,y,1*prop,0,2*Math.PI,false);

            }else{

                clock.fillStyle="black";

                clock.arc(x,y,1*prop,0,2*Math.PI,false);

            }

            clock.fill();

        }

    }

    function hours(hour,minute){

        clock.save();//一定要先保存

        clock.beginPath();

        var rad=2*Math.PI/12*hour;

        var minute_rad=2*Math.PI/12/60*minute;

        clock.rotate(rad+minute_rad);

        clock.strokeStyle="blue";

        clock.lineCap="round";

        clock.lineWidth=5*prop;

        clock.moveTo(0,2*prop);

        clock.lineTo(0,-r+40*prop);

        clock.stroke();

        clock.restore();//恢复

    }

    function minutes(minute){

        clock.save();

        clock.beginPath();

        clock.strokeStyle="orange";//设置路径的颜色

        clock.lineWidth=4*prop;

        clock.lineCap="round";//设置线的样式

        var rad=2*Math.PI/60*minute;

        clock.rotate(rad);//旋转画布

        clock.moveTo(0,5*prop);//将“画笔”移动到（这里没有绘画）

        clock.lineTo(0,-r+25*prop);

        clock.stroke();

        clock.restore();

    }

    function seconds(second){

        clock.save();

        clock.beginPath();

        clock.fillStyle="red";

        var rad=2*Math.PI/60*second;

        clock.rotate(rad);

        clock.moveTo(-2*prop,5*prop);

        clock.lineTo(2*prop,5*prop);

        clock.lineTo(1*prop,-r+18*prop);

        clock.lineTo(3*prop,-r+18*prop);

        clock.lineTo(0,-r+10*prop);

        clock.lineTo(-3*prop,-r+18*prop);

        clock.lineTo(-1*prop,-r+18*prop);

        clock.fill();

        clock.restore();

    }

    function middle_dot(){

        clock.beginPath();

        clock.fillStyle="white";

        clock.arc(0,0,5*prop,0,2*Math.PI,false);

        clock.fill();

    }

    function all(){

        clock.clearRect(0,0,width,height);

        outline();

        middle_dot();

        var now=new Date();//通过Date对象获取时间

        var hour=now.getHours();//获取当前小时数

        var minute=now.getMinutes();

        var second=now.getSeconds();

        hours(hour,minute);

        minutes(minute);

        seconds(second);

        clock.restore();

    }

    all();

    setInterval(all,1000);//使用定时器不断更新时间

     

};