how to perform a multiplication operation based on value from dropdownlist, using javascript?

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i have two labels and a dropdownlist..dropdownlist contains many numerical values.when user selects any dropdownlist value,that value should be multiplied with a constant number(which i retrieved here from database) and the result should change immediately on each user click. i used label7(hidden label) for retrieving a constant numerical value from database,and label4(visible label) for displaying the result after multiplication..here im getting a NaN as result...after writing the following code....

XML

<asp:Label ID="Label4" runat="server" style="color:white;font-size:medium;font-weight:bold;"></asp:Label><asp:Label ID="Label7" runat="server" style="color:white;font-size:medium;font-weight:bold;visibility:hidden;"></asp:Label>

<asp:DropDownList ID="DropDownList1" runat="server" Width="50px" onchange="mul()">
        <asp:ListItem>1
        <asp:ListItem>2
        <asp:ListItem>3
        <asp:ListItem>4
        <asp:ListItem>5
        <asp:ListItem>10
        <asp:ListItem>20
 

<script type="text/javascript">
      function mul() {
          var lab = document.getElementById('<%= Label7.ClientID %>');
          var lab1 = document.getElementById('<%= DropDownList1.ClientID %>');
 document.getElementById('<%=Label4.ClientID%>').innerHTML = parseInt(lab) * parseInt(lab1);
      }
      </script>
 finally my c# code
        Label4.Text = dt.Rows[0][3].ToString();
        Label7.Text =  dt.Rows[0][3].ToString();

Posted 19-Jun-14 1:20am

faizel s

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3 solutions

Solution 1

1) You must give comprehensible names to your variables
2) You did not extract any value of your controls so far
3) You have to use display instead of visibility to retrieve the value of your label

C#

function mul() {
    var lblVisible = document.getElementById('<%= lblVisible.ClientID%>');
    var lblHiddenValue = document.getElementById('<%= lblHidden.ClientID%>').innerText;
    var selectedValueFromDdl = document.getElementById('<%= ddlSelection.ClientID %>').value;
    lblVisible.innerText = parseInt(lblHiddenValue) * parseInt(selectedValueFromDdl);
}

XML

<asp:Label ID="lblVisible" runat="server" style="color:white;font-size:medium;font-weight:bold;"></asp:Label>
<asp:Label ID="lblHidden" runat="server" style="color:white;font-size:medium;font-weight:bold;display:none;"></asp:Label>
<asp:DropDownList ID="ddlSelection" runat="server" Width="50px" onchange="mul()">
    <asp:ListItem>1</asp:ListItem>
    <asp:ListItem>2</asp:ListItem>
    <asp:ListItem>3</asp:ListItem>
    <asp:ListItem>4</asp:ListItem>
    <asp:ListItem>5</asp:ListItem>
    <asp:ListItem>10</asp:ListItem>
    <asp:ListItem>20</asp:ListItem>
</asp:DropDownList>

Posted 19-Jun-14 2:10am

pjaar89

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NitinDhapte · Accepted Answer · 2014-06-19T02:20:00

Try This :

XML

<asp:DropDownList ID="DropDownList1" runat="server" Width="50px" onchange="mul()">
    <asp:ListItem Text="One" Value="1">One</asp:ListItem>
    <asp:ListItem Text="Two" Value="2">Two</asp:ListItem>
    <asp:ListItem Text="Three" Value="3">Three</asp:ListItem>
    <asp:ListItem Text="Four" Value="4">Four</asp:ListItem>
</asp:DropDownList>

Javascript Code :
-------------------

JavaScript

function mul() {
    var lab = document.getElementById('<% =Label7.ClientID %>');
    var lab1 = document.getElementById('<% =DropDownList1.ClientID %>');
    document.getElementById('<% =Label4.ClientID %>').innerHTML = parseInt(lab.innerHTML) * parseInt(lab1.value);
}

Peter Leow · Accepted Answer · 2014-06-19T03:23:00

Solution 3

Try some changes:

<asp:ListItem>1</asp:ListItem>

document.getElementById('<%= Label4.ClientID %>').innerHTML = parseInt(lab.innerHTML) * parseInt(lab1.options[lab1.selectedIndex].value);

Posted 19-Jun-14 3:23am

Peter Leow

Updated 19-Jun-14 3:27am

v2