sample code for setting mystjs parser options in jupyterlab extension

index.ts

import { JupyterFrontEnd, JupyterFrontEndPlugin } from '@jupyterlab/application';

import { IMySTNotebookOptions } from 'jupyterlab-myst';
import { MySTNotebookDefaults } from 'jupyterlab-myst/lib/myst';

import { proofsDirective } from './directives';

export class MyNotebookDefaults extends MySTNotebookDefaults {

  get(notebook: any) {
    const defaults = super.get(notebook);
    const directives = defaults.parserOptions.directives || [];
    defaults.parserOptions.directives = [...directives, proofsDirective];
    return defaults;
  }
}

const plugin: JupyterFrontEndPlugin<MyNotebookDefaults> = {
  id: 'monkey:plugin',
  autoStart: true,
  provides: IMySTNotebookOptions,
  activate: (app: JupyterFrontEnd) => {
    console.log('JupyterLab extension monkey is activated!');
    return new MyNotebookDefaults();
  }
};

export default plugin;