大家帮小弟我看看，如何获取这个文本框的焦点

大家帮我看看，怎么获取这个文本框的焦点
文本内容编辑是用的FCK，这是在HTML页面中查看源码得到的结果：

HTML code

<!--

Code highlighting produced by Actipro CodeHighlighter (freeware)
http://www.CodeHighlighter.com/

-->
<td width="100%" id="arcBody">
      <input type="hidden" id="body" name="body" value="请输入文本内容" style="display:none" />
      <input type="hidden" id="body___Config" value="FullPage=FALSE" style="display:none" />
      <iframe id="body___Frame" src="www.5i5qq.com/editor/fckeditor.html?InstanceName=body&Toolbar=Basic" width="100%" height="450" frameborder="0" scrolling="no"></iframe>    </td>
<td width="255" align="center" valign="top" bgcolor="#FFFFCC" id="mPic" style="display:none"><div class="multipic">
      <div style="display: block;background-color:#E5F1CF; height:26px"><span id="spanButtonPlaceholder"></span></div>
      <div id="divFileProgressContainer"></div>
      <div id="thumbnails" style="width: 254px; height: 535px; background-color: rgb(255, 255, 255); overflow-y: scroll;"></div>
</td>

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