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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<!DOCTYPE html>
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<html>
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<head>
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<style>
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table,th,td
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{
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border:1px solid black;
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}
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</style>
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</head>
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<body>
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​
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<h3>关于如何访问 COL 元素的一个演示</h3>
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​
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<table>
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  <colgroup>
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    <col id="myCol" span="2" style="background-color:red">
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    <col style="background-color:yellow">
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  </colgroup>
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  <tr>
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    <th>ISBN</th>
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    <th>Title</th>
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    <th>Price</th>
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  </tr>
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  <tr>
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    <td>3476896</td>
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    <td>My first HTML</td>
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    <td>$53</td>
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  </tr>
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  <tr>
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    <td>5869207</td>
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    <td>My first CSS</td>
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    <td>$49</td>
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  </tr>
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</table>
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​
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<p>请点击按钮，来获得 COL 元素应该横跨的列数。</p>
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​
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<p id="demo"></p>
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​
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<button onclick="myFunction()">试一下</button>
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​
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<script>
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function myFunction()
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{
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var x = document.getElementById("myCol").span;
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document.getElementById("demo").innerHTML = x;
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}