Triggering a postback from Javascript fails

I am trying to trigger a postback if a certain condition is true. Initially, a user will click on a button on my form, the server does some work, and in the process of doing that work it assigns a hidden field the value of '1'. When the page reloads after that very first postback, I am trying to use javascript to check the hidden field, and if it is '1' I need the page to postback again so the server side can do some additional processing. The reason for doing it this roundabout way is so that 开发者_JS百科I can create controls on the form from my C# code behind as well as download a file in 1 user interaction. Here is what I have so far:

<script type="text/javascript" language="JavaScript">
        function atload() {
            var HWInfo = document.getElementById('HiddenHW').value;
            if (HWInfo == '1') {
                alert("flag has been set");

                __doPostBack('<%= hdnHidden.UniqueID  %>', '');
             }

        }
        $(document).ready(atload);

    </script>

The alert that says the flag has been set correctly fires, but the __doPostBack does not. In my ASPX file, here is the relevant part:

 <form id="InventoryForm" runat="server">

<div>
    <asp:Label ID="lblClientList" runat="server" Text="Client List"></asp:Label>
    <asp:DropDownList ID="comboClientList" runat="server"></asp:DropDownList>
    <asp:Label ID="spacer1" runat="server" Text="     "></asp:Label>
    <asp:Button ID="btnGenerateHWReport" runat="server" Text="Generate Hardware Inventory Report" />
    <asp:Label ID="spacer2" runat="server" Text="     "></asp:Label>
    <asp:Button ID="btnGenerateSWReport" runat="server" Text="Generate Software Inventory Report" />
    <br />
    <br />

    <asp:Panel ID="MissingCompPanel" runat="server"></asp:Panel>
    <asp:HiddenField ID="HiddenHW" runat="server" Value="0" />
    <asp:HiddenField ID="hdnHidden" runat="server" />

</div>
</form>

I can tell the postback never fires, because I have breakpoints in the Page_Load C# codebehind that never get tripped. I have break points on almost every single line of this:

        if (!Page.IsPostBack)
        {
            // Page is not a postback, this is the first visit here
            string foo = HiddenHW.Value;
        }
        else
        {
            // Page is a postback and not initial load
            string foo = HiddenHW.Value;
        }

Why is my __doPostBak after the alert not firing, and is there a better way to do this? The end result I want is if my hidden field is '1', then I want my 2nd trip to the server to 1) actually happen and 2) know that the hidden field is '1' and not its default '0'.

Thanks!

how about just clicking the submit button programatically and have it call __doPostBack the way it normally does?

Try invoking the __doPostBack method on the page instead of the hidden control

__doPostBack('__Page', '');

When you get the value of HiddenHW, you're not using the right ID. If you look at the rendered source, the ID of the control is something like ctl00_HiddenHW. To get that ID, you should use HiddenHW.ClientID. I believe __doPostBack also needs the ClientID, not UniqueID.

function atload() {
    var HWInfo = document.getElementById('<%= HiddenHW.ClientID %>').value;
    if (HWInfo == '1') {
        alert("flag has been set");

        __doPostBack('<%= hdnHidden.ClientID %>', '');
    }
}