Setting value for javascript variable from code behind (C#)

I understand the difference between Client-side and Server-side scripting. I have a javascript function and variable in my MasterPage:

<script language="JavaScript" type="text/javascript">
    var needToConfirm = false;
          window.onbeforeunload = confirmExit;
          function confirmExit()
          {
            if (needToConfirm)
            {
              needToConfirm = false;
              return "Currently in edit mode. If you leave the page now then you will lose unsaved changes."
            }
          }
</script>

Given the fact that on my ASP.NET (Client-side) I can change the value of my needToConfirm variable to true onClientClick but by default it is false. Here's an example.

 <asp:Button ID="btnEdit" runat="server" Text="  Edit  " onclick="btnEdit_Click" OnClientClick="needToConfirm = true;" />

Now the question here is when on the C# (Server-side) I have to set the needToConfirm to true under an if-statement but not necessarily on Page_Load:

private void SetDefault()

    if (Session[def.ID_CUST] != null)
    {
          //I want to change the variable value here
    }
}

Thanks.

UPDATE

I'm using .NET 2.0 Classic and WebForms

Answers


in code behind:

ScriptManager.RegisterStartupScript(this, this.GetType(), "", "urFunction('urValHere');", true);

on client-side:

function urFunction(urParam) {
        //do what u want here
        //use urParam
    }

You can use a hidden input and then set this input to true or false from the server side.

On the client side:

<input type="hidden" id="hdnConfirm" runat="server" value="false"/>

Then on the server side:

 if (Session[def.ID_CUST] != null)
    {
          //I want to change the variable value here
           hdnConfirm.Value = "true";
    }

Then on the client side:

var needToConfirm = $('#hdnConfirm').val();

If I understand this correctly, you could register a client script like in the example at http://msdn.microsoft.com/en-us/library/z9h4dk8y.aspx.

ClientScriptManager cs = Page.ClientScript;
if (!cs.IsStartupScriptRegistered(this.GetType(), "EditMode")) {
    cs.RegisterStartupScript(this.GetType(), "EditMode", "needToConfirm = true;", true);
}

That would write a script to the page setting the value of needToConfirm in Javascript.


Based on your update saying it's .NET 2.0, this is how you can set a javascript variable:

Page.RegisterStartupScript("SetVar", "var needToConfirm = true;");

http://msdn.microsoft.com/en-us/library/system.web.ui.page.registerstartupscript(v=vs.80).aspx


Just for reference. Here is the 4.5 way to do something like this:

 // Define the name and type of the client scripts on the page.
 const String csname1 = "MyScriptName";
 Type cstype = this.GetType();

 // Get a ClientScriptManager reference from the Page class.
 ClientScriptManager cs = Page.ClientScript;

 // Check to see if the startup script is already registered.
 if (!cs.IsStartupScriptRegistered(cstype, csname1))
 {
      StringBuilder cstext1 = new StringBuilder();
      cstext1.Append("<script> var myVariable = true; </");
      cstext1.Append("script>");

      cs.RegisterStartupScript(cstype, csname1, cstext1.ToString());
  }

http://msdn.microsoft.com/en-us/library/system.web.ui.clientscriptmanager.registerstartupscript(v=vs.110).aspx


Maby this helps?

<script type="text/javascript">
    function test(confirm){
        var needToConfirm = confirm;
        window.onbeforeunload = confirmExit;
        function confirmExit() {
            if (needToConfirm) {
                needToConfirm = false;
                return "Currently in edit mode. If you leave the page now then you will lose unsaved changes."
            }
        }
    }
</script>



<asp:Button ID="btnEdit" runat="server" Text="Edit" onclick="btnEdit_Click" OnClientClick="javascript:test(true);" />

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