TS Deployed SPAppWeb

var qsKeys = Request.QueryString.AllKeys;
 
if (qsKeys.Contains("SPAppWebUrl"))
{
    AppWebUrl.Value = Request.QueryString["SPAppWebUrl"];
}
else
{
    var rootUri = new UriBuilder(String.Concat(new Uri(Request.QueryString["SPHostUrl"]).Authority, "/sites/apps"))
    {
        Scheme = Uri.UriSchemeHttps,
        Port = 443
    };
 
    SharePointOnlineHelper.RunInNewAppOnlyContext(rootUri.ToString(), appCtx =>
    {
        var web = appCtx.Web;
        var appInstances = web.GetAppInstances();
 
        var target = appCtx.LoadQuery(appInstances.Where(a => a.Title == "Site Konfigurator"));
        appCtx.ExecuteQuery();
 
        AppWebUrl.Value = target.Single().AppWebFullUrl;
    });
}

And then pick it up via a asp hiddenfield

<asp:HiddenField ID="AppWebUrl" ClientIDMode="Static" runat="server" />

var appweburl = $('#AppWebUrl').val();