请教一个js判断问题


<object type="application/x-shockwave-flash" data="vcastr3.swf" width="554" height="310" id="vcastr3">
        <param name="movie" value="vcastr3.swf" />
        <param name="allowFullScreen" value="true" />
        <param name="FlashVars" value="xml=
<vcastr>
        <config>
<bufferTime>4</bufferTime>
<contralPanelAlpha>0.7</contralPanelAlpha>
<controlPanelBgColor>0x000000</controlPanelBgColor>
<controlPanelBtnColor>0xffffff</controlPanelBtnColor>
<contralPanelBtnGlowColro>0xffff00</contralPanelBtnGlowColro>
<controlPanelMode>normal</controlPanelMode>
<defautVolume>0.58</defautVolume>
<isAutoPlay>ture</isAutoPlay>
<isLoadBegin>false</isLoadBegin>
<isShowAbout>false</isShowAbout>
<scaleMode>showAll</scaleMode>
<isRepeat>false</isRepeat>
</config>
<plugIns>
<beginEndImagePlugIn>
<url>beginEndImagePlugIn.swf</url>
<source>[!--bnimage--]</source>
<type>begin</type>
<scaleType>exactFit</scaleType>
</beginEndImagePlugIn>
</plugIns>
          <channel>
<item>
<source>[!--flvurl--]</source>
</item>
</channel>

</vcastr>"/>
      </object>  
[!--flvurl--]为帝国的一个标签，当这个标签为空的时候，把这一段代码隐藏。求解！！！！