Limit maximum characters in textbox (textarea) and display remaining count using javascript in C# Asp.Net

function Count(text, long) {
          var maxlength = new Number(long); // Change number to your max length.
          if (text.value.length > maxlength) {
              text.value = text.value.substring(0, maxlength);
              //alert(" Only " + long + " chars");
          }
          //Display remaining count
          //ctl00_ContentPlaceHolder1_lblCount.innerHTML = maxlength - text.value.length;
          var lblMsg = $get('<%= lblCount.ClientID %>');
          lblMsg.innerHTML = maxlength - text.value.length;
      }

<asp:TextBox ID="TextBox1" TextMode="MultiLine" runat="server" onKeyUp="javascript:Count(this,10);" onChange="javascript:Count(this,10);" ></asp:TextBox>
    <br />
    <asp:Label ID="lblCount" runat="server" Text="10"></asp:Label>