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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<html>
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<head>
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<script type="text/javascript">
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function changeAlt()
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  {
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  document.getElementById("compman").alt="Man using computer"
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  }
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function alertAlt()
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  {
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  alert(document.getElementById("compman").alt)
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  }
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</script>
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</head>
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<body>
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​
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<img id="compman" src="/img/eg_compman.gif" alt="Computerman" />
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<br />
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<input type="button" onclick="changeAlt()" value="Change alt text">
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<br /><br />
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<input type="button" onclick="alertAlt()" value="Alert alt text">
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​
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</body>
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</html>
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​