In my ASCX, I have an asp.net hidden field defined as <asp:HiddenField ID="hdnNewAsset" runat="server" />.

In the Code Behind I have the following code:

    protected void Page_Load(object sender, EventArgs e)
    {
        _service = new ArticleDataService(PortalId);

        if (!IsPostBack)
        {
            string rawId = Request[ArticleQueryParams.ArticleId];
            DisplayArticleDetails(rawId);
        }

        if (hdnNewAsset.Value.Trim() != string.Empty)
            ProcessNewAsset();
    }

Now, in my frontend, I have a javascript function to react to an event and set the hidden field and trigger a postback:

function assetSelected(assetGuid) {
    $('input[id*="hdnNewAsset"]').val(assetGuid);
    __doPostBack()
}

What's happening is that my hidden field is being set in the markup (chrome shows [ <input type=?"hidden" name=?"dnn$ctr466$Main$ctl00$hdnNewAsset" id=?"dnn_ctr466_Main_ctl00_hdnNewAsset" value=?"98d88e72-088c-40a4-9022-565a53dc33c4">? ] for $('input[id*="hdnNewAsset"]')).

However, when the postback occurs, hdnNewAsset.Value is an empty string.

What's even more puzzling is that at the beginning of Page_Load Request.Params["dnn$ctr466$Main$ctl00$hdnNewAsset"] shows 98d88e72-088c-40a4-9022-565a53dc33c4, and after the postback my hidden field has the same value (so the hidden field is persisting across postbacks), yet I cannot access this value via hdnNewAsset.Value.

Can anyone see what I"m doing wrong?