Count number of characters in textbox

Markup Page

<strong>Required Info:</strong> 
<asp:Label ID="TotCharReqInfo" runat="server" ></asp:Label>  

<strong>Body Length:</strong> 
<span id="BodyLength">0

<strong>Total Length:</strong> <span id="TotLength"> 
<asp:Label ID="TotLengthLbl" runat="server" ></asp:Label>

<strong>Left:</strong> <span id="CharLeft">
<asp:Label ID="ChLeft" runat="server" ></asp:Label>


<asp:TextBox id="txtInputOnln" runat="server" 
    TextMode="MultiLine" Width="300px" Height="90px" 
    MaxLength="350" onKeyUp="Count(this,350)" 
    onChange="Count(this,350)"/>

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<script type="text/javascript">
   var ChLeftVar = "<%=CharLeftInt %>";
   var ChLeftOut
   var ChLefVar2
   function count(clientId) {
     var txtInputOnln = document.getElementById(clientId);
     var CharLeft = document.getElementById('CharLeft');
     var BodyLength = document.getElementById('BodyLength');
     var TotLength = document.getElementById('TotLength');
                        
     BodyLength.innerHTML = txtInputOnln.value.length;
     ChLeftOut = 350 - ChLeftVar
     ChLeftVar2 = (350 - ChLeftOut) + txtInputOnln.value.length;
     TotLength.innerHTML = ChLeftVar2;
     CharLeft.innerHTML = ChLeftOut - txtInputOnln.value.length;
     }
//limit user input (350 this case)
    function Count(text, long) {
      var maxlength = new Number(ChLeftOut); // Change number to your max length.
         if (text.value.length > maxlength) {
         text.value = text.value.substring(0, maxlength);
         // alert(" Only " + long + " chars");//
         alert(" Only 350 characters ");
         }
       }
</script>


Code Behind

Protected CharLeftStr As String
Protected CharLeftInt As Integer

Dim count As Integer = 0
Dim ReqInfoTot As String = TxtBx1.Text + TxtBx2.Text + TxtBx3

For Each c As Char In ReqInfoTot
    If Char.IsLetter(c) Or Char.IsNumber(c) Then
        count += 1
     End If
Next

TotCharReqInfo.Text = count.ToString() - 2
TotLengthLbl.Text = count.ToString() - 2
'(2) is number of "+" inside the ReqInfoTot string
txtInputOnln.Attributes("onkeydown") = 
            = String.Format("count('{0}')", txtInputOnln.ClientID)
       
ChLeft.Text = 350 - TotCharReqInfo.Text.ToString()
CharLeftStr = TotCharReqInfo.Text.ToString()
CharLeftInt = Convert.ToInt32(CharLeftStr)