Javascript Question posted in
A very good W3school tutorial can be found here.

cant send javascript variable to server-side code behind

i want to send value (which is in my javascript) to an asp hiddenfield value so i can access the variable in code behind (C#).

so i have a hiddenfield:

<asp:HiddenField id="SendA" value="ee" runat="server" />

and in my javascript:

function test2() {
    
    document.getElementById("<%=SendA.ClientID%>").value = "nice";
    alert(document.getElementById("<%=SendA.ClientID%>").value);
}

but the console says: JavaScript.js:76 Uncaught TypeError: Cannot set properties of null (setting ‘value’)
at test2.

i have the right syntax and it should alert nice , whats my problem?

Tags:

2

Answers


  1. 0

    Ensure that your JavaScript code is placed after the HiddenField in the rendered HTML or that it’s executed after the DOM has fully loaded. I mean; you may need something like that:

    <script>
    // if you have jQuery
    $(document).ready(function() {
        test2();
    });

    // if not
    document.addEventListener("DOMContentLoaded", function() {
        test2();
    });
</script>
    Login or Signup to reply.
  2. 0

    What you posted should work. You don’t show how you calling that JavaScript function.

    With this markup:

    <asp:HiddenField ID="SendA" Value="ee" runat="server" />

<br />

<asp:Button ID="cmdShow" runat="server" Text="set and show value"
    OnClientClick="test2();return false;" />


<script>

    function test2() {

        document.getElementById("<%=SendA.ClientID%>").value = "nice";
        alert(document.getElementById("<%=SendA.ClientID%>").value);
    }

</script>

    The result works and is this:

    enter image description here

    So, this suggests your markup or JavaScript code has some errors, or is incorrectly placed on the page.

    Create a blank new test page, and try the above code, or your code – it should work just fine.

    Login or Signup to reply.
Please signup or login to give your own answer.

Back To Top
Search