案例：javascript案例     状态：可编辑再运行    进入竖版
 运行结果　
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<html>
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<body>
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<iframe src="/example/hdom/frame_a.html" id="frame1" marginwidth="50"></iframe>
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<br /><br />
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​
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<script type="text/javascript">
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x=document.getElementById("frame1");
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document.write("Left and right margins of the iframe are: ");
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document.write(x.marginWidth);
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</script>
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​
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</body>
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</html>
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​