Calling javascript from Codebehind

I have read many different resources but am still not sure if this is possible without using AJAX.

I have a javascript function that loads a div into a modal and says "Loading Please Wait" I have named this funciton loadingModal()

function loadingModal(url)
{
     loadModal(...)
}

What I need to do is only trigger this after I have verified that the password and username are correct on the server side so:

btnSubmit_OnClick(object sender EventArgs e)
{
     string usr;
     string password;

     if (verify(usr, password))
     {
          ///// TRIGGER JAVASCRIPT HERE
          LOAD TONS OF SESSION VARIABL开发者_如何学PythonES
          .
          .
          .
      }
      else
         Show Error and Definitely Don't ever mention still loading
 }

I know I could just attach an onclientclick call to the javascript however it would load the loading modal even if it was an invalid username and password

Can I trigger javascript mid execution from the server side?

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Can I trigger JavaScript mid execution from the server side?

No. JavaScript code is evaluated on the client-side (in the browser), long after the server-side has finished processing the request. Client-side and server-side scripts are run at different places and at different times. There cannot be that kind of direct interaction.

You could use AJAX, if you do not want to trigger a full page refresh. When you use AJAX, your client (the browser) will issue a fresh new request to the server. The server processes this request (checks username and password, for example) and returns a response (access denied or access granted) back to the client. It is then up to the client to handle the response appropriately.

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If you mean add javascript code to the page, see ScriptManager.RegisterStartupScript

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Hope its not too late...

Your best bet is to add 2 asp:Panel: One with a Ajax loading gif that is normally visible until the page is ready and one with style="display:none" and an asp:Label within that panel.

In code-behind, when validation is false, you just change the style to display:inline and set the text of the label to whatever you need. And of course, exit sub without displaying your modal thingy!

Here's an example:

<asp:Panel ID="pnlError" runat="server" style="display:none; position:absolute; left:300; top:300; width:300;">
    <asp:Label ID="lblErr" runat="server" style=" color:Red;"></asp:Label>
</asp:Panel>

If validation = false Then
        lblErr.Text = "Wrong user name or password or whatever!..."
        pnlLoading.Style.Item("display") = "none"
        pnlError.Style.Item("display") = "inline"
        Exit Sub
End if

This way your user will see the loading gif, knowing "something" is in poreparation, and if wrong, he is warned.