<script type="text/javascript">

window.onload = function() {

// 初始化

var canvas  = document.getElementById("canvas");

var context = canvas.getContext("2d");

// 画布设置

canvas.width = 800;

canvas.height = 800;

   context.fillStyle = "black";

   context.fillRect(0,0,canvas.width,canvas.height);

  // 绘画星星

// 星星参数

for(var i = 0; i <=200; i++)

{

var r = Math.random()*40+20;

var x = Math.random()*canvas.width;

var y = Math.random()*canvas.height;

var a = Math.random()*360;

draw(context,x,y,r,a);

}

}

function draw(cxt,x,y,r,rot){

cxt.save();

cxt.translate( x , y );

cxt.rotate(rot/180 * Math.PI);

star(cxt);

cxt.fillStyle = "#fb3";

cxt.strokeStyle = "#fd5";

cxt.lineWidth = 3;

cxt.lineJoin = "round";

cxt.fill();

cxt.stroke();

cxt.restore();

}

function star(cxt){

cxt.beginPath();

for(var i = 0; i < 5; i++){

cxt.lineTo(Math.cos((18+i*72)/180*Math.PI*20),

 -Math.sin((18+i*72)/180*Math.PI)*20 );

cxt.lineTo(Math.cos((54+i*72)/180*Math.PI)*0.5*20,

-Math.sin((54+i*72-)/180*Math.PI)*0.5*20);

}

cxt.closePath();

}

</script>