Count number of characters in TextBox on keyup event and display in Label using jQuery in ASP.Net

 @nedash,

Try following...

<script type="text/javascript">
        function CountChar(txtmsg) {
            var count = document.getElementById(txtmsg).value.length;
            if (count > 1 && count <= 160) {
                document.getElementById('charstatus').innerHTML = 160 - document.getElementById(txtmsg).value.length;
            }
            if (document.getElementById(txtmsg).value.length > 160 - 1) {
                document.getElementById('charstatus').innerHTML = "Maximum characters reached!";
            }
        }
        </script>

<div class="col-md-6">
                    <div class="form-group">
                        <label>Enter the message you want to set</label>
                        <textarea id="txtmsg" runat="server" class="form-control" maxlength="160" rows="3"
                         placeholder="Message content should not exceed 160 characters."
                         onkeyup="CountChar(this.id);"></textarea>
                            <asp:CheckBox ID="chkdefault" CausesValidation="true" AutoPostBack="true" ToolTip="Set this message as default for the selected area." runat="server" Text="Set this message as default" />
                        <div class="pull-right">
                            <p>Characters remaining: <button class="btn btn-default disabled" id="charstatus"></button></p>
                        </div>
                        
                    </div>
                </div>