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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<form id="form1">
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<input type="checkbox" id="check1" />
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</form>
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​
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<p>The form containing the checkbox is:
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<script type="text/javascript">
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x=document.getElementById('check1');
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document.write(x.form.id);
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</script></p>
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​
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</body>
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</html>
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​