案例：html案例     状态：可编辑再运行    进入竖版
 运行结果　
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<!DOCTYPE HTML>
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<html>
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<body>
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​
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<canvas id="myCanvas" width="200" height="100" style="border:1px solid #c3c3c3;">
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Your browser does not support the canvas element.
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</canvas>
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​
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<script type="text/javascript">
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​
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var c=document.getElementById("myCanvas");
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var cxt=c.getContext("2d");
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cxt.fillStyle="#0000FF";
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cxt.beginPath();
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cxt.arc(70,18,15,0,Math.PI*2,true);
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cxt.closePath();
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cxt.fill();
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​
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</script>
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​
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</body>
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</html>