                        课程
                    
                        /前端开发
                        
                            /Html5
                        
                        /炫丽的倒计时效果Canvas绘图与动画基础

为什么我的七巧板的代码在浏览器里的显示只是个灰色的框

代码是按照老师视频里写的，请问是哪里出问题了

<!DOCTYPE html>
<html>
<head lang="en">
<meta charset="UTF-8">
<title>七巧板</title>
</head>
<body>
<canvas id="canvas" style="border: 1px solid #aaa;display: block;margin: 50px auto;">
当前浏览器不支持Canvas，请更换浏览器后再试
</canvas>

<script>
var tangram = [
{P:[{x:0,y:0},{x:800,y:0},{x:400,y:400}],color:"#caff67"},
{P:[{x:0,y:0},{x:400,y:400},{x:0,y:800}],color:"#67becf"},
{P:[{x:800,y:0},{x:800,y:400},{x:600,y:600},{x:600,y:200}],color:"#ef3d61"},
{P:[{x:600,y:200},{x:600,y:600},{x:400,y:400}],color:"#f9f51a"},
{P:[{x:400,y:400},{x:600,y:600},{x:400,y:800},{x:200,y:600}],color:"#a594c0"},
{P:[{x:200,y:600},{x:400,y:800},{x:0,y:800}],color:"#fa8ecc"},
{P:[{x:800,y:400},{x:800,y:800},{x:400,y:800}],color:"#f6ca29"},
]
window.onload = function () {
var canvas = document.getElementById("canvas");

canvas.width = 800;
canvas.height = 800;

var context = canvas.getElementById("2d")
for(var i = 0;i<tangram.length;i++)
draw(tangram[i],context)
}

function draw(piece,cxt){

cxt.beginPath();
cxt.moveTo(piece.p[0].x,piece.p[0].y);
for(var i=1;i<piece.p.length;i++)
cxt.lineTo(piece.p[i].x,piece.p[i].y);
cxt.closePath();

cxt.fillStyle = piece.color;
cxt.fill();
}
</script>
</body>
</html>