按視頻的腳本，但是顯示空白
顯示一片空白，求大神解答
<!DOCTYPE html>
<html>
<head ?>
? <meta charset="utf-8">
? <title>canvas倒計時繪制</title>
</head>
<body>
<canvas id="canvas" ?style="border:1px solid #aaa; display:block; margin:0 auto;">
當前瀏覽器不支持canvas，請更換瀏覽器后再試
</canvas>
</body>
<script>
?window.onload = function(){
var canvas=document.getElementById("canvas");
canvas.width="1024";
canvas.height="768";
?
var context=canvas.getContext("2d")
//使用context繪制
context.moveTO(100,100)
context.lineTo(700,700)
context.lineTo(100,700)
context.lineTo(100,100)
context.lineWidth=5
context.stroleStyle="#005588"
context.stroke()
}
</script>
</html>
