html
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title></title>
<script type="text/javascript" src="23.js"></script>
</head>
<body onBlur="draw('canvas');">
<canvas id="canvas" width="500" height="350"></canvas>
</body>
</html>
js
// JavaScript Document
效果图：