def METHOD_NAME():
    """
    Installs a periodic callback which checks for changes in watched
    files and sys.modules.
    """
    if not state.curdoc or not state.curdoc.session_context.server_context:
        return
    cb = partial(_reload_on_update, {})
    _callbacks[state.curdoc] = pcb = PeriodicCallback(callback=cb, background=True)
    pcb.start()