JSFiddle - React, Tailwind, and code Playground

HTML

<asp:TextBox ID="D1" runat="server"  Width="50px" CssClass="sum"></asp:TextBox>
  <asp:TextBox ID="D2" runat="server" Width="50px" CssClass="sum"></asp:TextBox>
  <asp:TextBox ID="D3" runat="server" Width="50px" CssClass="sum"></asp:TextBox>
<asp:TextBox ID="D4" runat="server" Width="50px" CssClass="sum"></asp:TextBox>
 <asp:TextBox ID="D5" runat="server" Width="50px" CssClass="sum"></asp:TextBox>


 Total Hours<asp:TextBox ID="Total" runat="server" Width="50px" ReadOnly="True" ClientIDMode=static"></asp:TextBox>

JavaScript

$('.sum').keydown(function(e) {
            //getting key code of pressed key
            var keycode = (e.which) ? e.which : e.keyCode;
            //comparing pressed keycodes
            if (!(keycode == 8 || keycode == 46) && (keycode < 48 || keycode > 57)) {
                e.preventDefault();
            }
        });

        $('.sum').keyup(function(e) {
            var total=0;
            var current;
            $('.sum').each(function(){
                current=parseInt($(this).val());
            if($.isNumeric(current))
            {
               total+=  current;              
            }
            });
            $("#text6").val(total);

        });