private void NS3420Browser_Navigating(object sender, System.Windows.Navigation.NavigatingCancelEventArgs e)
    {

        Console.WriteLine("URI:");
        Console.WriteLine(e.Uri);

        if (e.Uri.ToString().EndsWith(".json"))
        {
            e.Cancel = true;
            Console.WriteLine("json file!");
        }

    }

var data = {a:1, b:2, c:3};
var json = JSON.stringify(data);
var blob = new Blob([json], {type: "application/json"});

saveAs(blob, "test.json");