如何将textbox的值放入alertmessegebox javascript中

Question

    <asp:TextBox ID="txtCosttotal" Text="10" runat="server"></asp:TextBox>

this is my javascript code

<script>

 function GetValue() {

            var result = document.getElementById('<%=txtCosttotal.ClientID%>');
            alert("Your Total Cost is " + result);            

        }
</script>

my vb code the txtitemcost and requestedqty the value is coming from database

      Dim icost2 As Double = 0
        icost2 = Val(txtItemCost.Text) * Val(Txtrequestedqty.Text)
        txtCosttotal.Text = icost2


 ScriptManager.RegisterStartupScript(Me, [GetType](), "displayalertmessage", "GetValue();", True)

the output

" Your Total Cost is [object HTMLinputElement] "

Answer 1

Your function document.getElementById('<%=txtItemNumber.ClientID%>') returns the actual input element. If you want to get to the actual value you need to use property value :

function GetValue() {
    var result = document.getElementById('<%=txtItemNumber.ClientID%>').value;
    alert("Your Total Cost is " + result);
}

You can read more about value property