案例：javascript案例     状态：可编辑再运行    进入竖版
 运行结果　
​x
 
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<html>
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<body>
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​
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<iframe src="/example/hdom/frame_a.html" id="frame1" longdesc="index.html"></iframe>
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<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("Description for frame contents: ");
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document.write('<a href="' + x.longDesc + '">Description</a>');
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</script>
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​
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</body>
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</html>