SAP BSP页面里，每次在Text Area里敲字后如何统计输入的总字数

<%@page language="abap" %>
<%@extension name="thtmlb" prefix="thtmlb" %>
<%@extension name="chtmlb" prefix="chtmlb" %>
<%@extension name="bsp" prefix="bsp" %>
<%
  DATA: lv_id TYPE string VALUE '_socialpost_struct.content' .
  DATA: lv_title TYPE string.
  " will be replaced by OTR
  lv_title = 'the count you have input:'.
  lv_id = controller->component_id && lv_id.
%>
<chtmlb:config mode = "RUNTIME"
               xml  = "<%= controller->configuration_descr->get_config_data( ) %>" />
<br>
<p id="char"  style="margin-left:8px"></span>
<script>

var content;
var counter;
function handleClick()
{
  var sCount = "<%= lv_title %>" + content.value.length;
  counter.innerHTML = sCount;
}

function fillTitle()
{
  counter.innerHTML = "<%= lv_title %>";
}

window.onload = function(){
  content = document.getElementById("<%= lv_id %>");
  counter = document.getElementById("char");
  if( content != null )
  {
    content.onkeyup = handleClick;
    content.onkeydown = handleClick;
  }
  else
  {
    alert("content not found!");
  }
  fillTitle();
}
</script>