Value is concatenated instead of added using DevExpress controls

I’m new to using DevExpress controls and Javascript and would like to enter a value into 2 textboxes and for the result to be returned in the 3rd textbox. Code below:

         function sum() {
             var num1 = +txtValue1.GetValue();
             var num2 = +txtValue2.GetValue();
             var result = parseInt(txtValue1.GetValue) + parseInt(txtValue2.GetValue);             
         } 
        </script>
        <style type="text/css">
        #form1 {
            align-content: center;
            display: block;
            height: 288px;
            margin-top: 0px;
        }
    </style>
    <title></title>
</head>
<body>
    
    <form id="form1" runat="server">
    
         <div>
            Toms Test Form</div>
            
             <br />  
                <dx:ASPxLabel ID="lblValue1" ClientInstanceName="lblValue_1" runat="server" Text="Value 1:" ></dx:ASPxLabel> <br />
                <dx:ASPxTextBox ID="txtValue1" runat="server" Width="180px" Height="5px"> 
                    <ValidationSettings ValidationGroup="vgtxtValue1">
                        <RequiredField IsRequired="True" ErrorText="You must enter a value" />
                 </ValidationSettings>  
                </dx:ASPxTextBox>
                <dx:ASPxLabel ID="lblValue2" ClientInstanceName="lblValue2" runat="server" Text="Value 2:"></dx:ASPxLabel>
                <dx:ASPxTextBox ID="txtValue2" runat="server" Width="180px" Height="5px">
                    <ValidationSettings ValidationGroup="vgtxtValue2">
                     <RequiredField IsRequired="True" ErrorText="You must enter a value"/>
                    </ValidationSettings>
                </dx:ASPxTextBox> 
                <dx:ASPxLabel ID="lblTotal" runat="server" Text="Value Total:" ></dx:ASPxLabel>
                <dx:ASPxTextBox ID="txtTotal" runat="server" Width="180px" Height="5px" readonly="true"></dx:ASPxTextBox> <br />
                <dx:ASPxButton  ID="btnTotal" runat="server" Text="Calculate Total" >
                    <ClientSideEvents Click="sum"/></dx:ASPxButton>          
         <div />```