Gtk.Window.prototype.is_active

function is_active():Boolean {
    // Gjs wrapper for gtk_window_is_active()
}

Returns whether the window is part of the current active toplevel. (That is, the toplevel window receiving keystrokes.) The return value is true if the window is active toplevel itself, but also if it is, say, a Gtk.Plug embedded in the active toplevel. You might use this function if you wanted to draw a widget differently in an active window from a widget in an inactive window. See Gtk.Window.prototype.has_toplevel_focus

Since 2.4