Show number of characters remaining in TextArea inside Repeater using JavaScript in ASP.Net

Hi am Trying to count the character inside the Repeater Control of Text Box It is working fine if I will Placed the Text Box outside the Repeater Control.Please do something as needful.Here I attach the Code of Html and Java Script.how can count the character of text box inside Repeater.Kindly help me out.Here i will Take TextBox Id txtarea and count the character in Label id is lblcharcnt.

   <asp:Repeater ID="rpquery" runat="server" OnItemCommand="rpquery_ItemCommand"

  <asp:TextBox ID="txtarea" runat="server" Width="700px" Height="80px" TextMode="MultiLine" onkeyup="cnt()" MaxLength="1000"></asp:TextBox>
  <p style="text-align: right;">
    <asp:Label ID="lblcharcnt" runat="server" Text="1000"></asp:Label>

  </p>
  <asp:Label ID="lblcount" runat="server" Text='<%#Eval("row") %>' Visible="false"></asp:Label>


  </ItemTemplate>
</asp:Repeater>

<script type="text/javascript">
  function cnt() {
    var a = document.getElementById("txtarea").value;
    document.getElementById("lblcharcnt").innerHTML = 1000 - a.length;
  }
</script>