案例:javascript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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<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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<table>
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  <colgroup id="myColgroup"></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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<p>点击按钮,把前两列的背景色设置为红色。</p>
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<p id="demo"></p>
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<button onclick="myFunction()">试一下</button>
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<script>
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function myFunction()
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{
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document.getElementById("myColgroup").span="2";
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document.getElementById("myColgroup").style.backgroundColor="red";
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}
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</script>
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</body>
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</html>
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