giới hạn nhập từ trong form

**** script
<script type="text/javascript">
var setTotalNumberOfWordCounter = "100";
function displayWordCounter(){
var getTextValue = document.frm.dd_fc_comment.value;  // Get input textarea value
var getTextLength = getTextValue.length;   // Get length of input textarea value
if(getTextLength > setTotalNumberOfWordCounter){     //compare this length with total count
       getTextValue = getTextValue.substring(0,setTotalNumberOfWordCounter);
       document.frm.dd_fc_comment.value =getTextValue;
       return false;
}
document.frm.totalWordLimit.value = (setTotalNumberOfWordCounter-getTextLength);
}
</script>

****html
<form name="frm" method="POST">
<textarea name="dd_fc_comment" class="main_txt_area" onkeyup="return displayWordCounter();"></textarea><br>
<div class="total_count">total remaining Charatctor: <input class="show_count" name="totalWordLimit" size="4" readonly="" value="100" type="text"></div>
</form>