案例：jQuery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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<head>
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  <script type="text/javascript" src="/js/jquery.js"></script>
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</head>
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​
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<body>
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  <ul>
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    <li>list item 1</li>
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    <li>list item 2</li>
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    <li class="third-item">list item 3</li>
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    <li>list item 4</li>
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    <li>list item 5</li>
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  </ul>
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​
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<script>
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  $('li.third-item').prev().css('background-color', 'red');
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</script>
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​
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</body>
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</html>
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​