 /**
     * Register the mime type and append_mime function with output_area
     */
    OutputArea.prototype.register_mime_type(EXEC_MIME_TYPE, append_mime, {
      /* Is output safe? */
      safe: true,
      /* Index of renderer in `output_area.display_order` */
      index: 0
    });
  }

  // register the mime type if in Jupyter Notebook environment and previously unregistered
  if (root.Jupyter !== undefined) {
    const events = require('base/js/events');
    const OutputArea = require('notebook/js/