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><strong>list</strong> item 1 - one strong tag</li>
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  <li><strong>list</strong> item <strong>2</strong> -
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    two <span>strong tags</span></li>
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  <li>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").click(function() {
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  var $li = $(this),
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    isWithTwo = $li.is(function() {
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      return $('strong', this).length === 2;
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    });
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  if ( isWithTwo ) {
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    $li.css("background-color", "green");
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  } else {
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    $li.css("background-color", "red");
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  }
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});
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</script>
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​
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</body>
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</html>
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​