callbacks();
      return null;
    }
    console.debug("Bokeh: BokehJS not loaded, scheduling load and callback at", now());
    root._bokeh_is_loading = css_urls.length + js_urls.length;

    function on_load() {
      root._bokeh_is_loading--;
      if (root._bokeh_is_loading === 0) {
        console.debug("Bokeh: all BokehJS libraries/stylesheets loaded");
        run_callbacks()
      }
    }

    function on_error(url) {
      console.error("failed to load " + url);
    }

    for (let i = 0; i < css_