title: can't get textarea's scrollheight when delete contents
body: <p>I want to get the scrollheight of  <code>&lt;textarea&gt;</code>  when people changing the content.The problem is when I add the content ,I can get a growing scrollheight ，but when I delete contents,I can't get a Reduced scrollheight。And here is the code</p>
  
  <pre><code>$("textarea[id^='_sub_ialready_']").live("keydown keyup focus blur",
      function()
      {
          if(aobj.minHeight == 0)
          aobj.minHeight = $(this).height();
          if($(this).attr("scrollHeight") &gt; aobj.minHeight)
          {
              if($(this).attr("scrollHeight") &gt; aobj.maxHeight)
              {
                  nheight = aobj.maxHeight;
                  $(this).css("overflow-Y",'scroll');    
              }    
              else
              {
                  nheight = $(this).attr("scrollHeight");
                  $(this).css("overflow-Y",'hidden');    
              }
              $(this).height(nheight);
         }
      }
  )
  </code></pre>