<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Canvas练习</title>
<script type="text/javascript">
function clearMap(){
context.clearRect(0,0,300,200);
}
</script>
</head>
<body>
<canvas id="myCanvas" style="border:1px solid" width="300" height="150">
您的浏览器不支持canvas元素，请更新或更换您的浏览器。
</canvas>
<script type="text/javascript">
var c=document.getElementById("myCanvas");
var context=c.getContext("2d");
context.fillStyle="red";
context.beginPath();
context.arc(200,150,100,-Math.PI*1/6,-Math.PI*5/6,true);
context.stroke();
</script><br>
<input name="" type="button" value="清空画布" onClick="clearMap();">
</body>
</html>