How to use the @jupyterlab/application.JupyterLab function in @jupyterlab/application

require('@jupyterlab/markdownviewer-extension'),
    require('@jupyterlab/mathjax2-extension'),
    require('@jupyterlab/notebook-extension'),
    require('@jupyterlab/rendermime-extension'),
    require('@jupyterlab/running-extension'),
    require('@jupyterlab/settingeditor-extension'),
    require('@jupyterlab/shortcuts-extension'),
    require('@jupyterlab/statusbar-extension'),
    require('@jupyterlab/tabmanager-extension'),
    require('@jupyterlab/terminal-extension'),
    require('@jupyterlab/theme-dark-extension'),
    require('@jupyterlab/theme-light-extension'),
    require('@jupyterlab/tooltip-extension'),
    require('@jupyterlab/ui-components-extension')
  ];
  var lab = new JupyterLab();
  lab.registerPluginModules(mods);
  /* eslint-disable no-console */
  console.log('Starting app');
  await lab.start();
  console.log('App started, waiting for restore');
  await lab.restored;
  console.log('Example started!');
});

require('@jupyterlab/markdownviewer-extension'),
    require('@jupyterlab/mathjax2-extension'),
    require('@jupyterlab/notebook-extension'),
    require('@jupyterlab/rendermime-extension'),
    require('@jupyterlab/running-extension'),
    require('@jupyterlab/settingeditor-extension'),
    require('@jupyterlab/shortcuts-extension'),
    require('@jupyterlab/statusbar-extension'),
    require('@jupyterlab/tabmanager-extension'),
    require('@jupyterlab/terminal-extension'),
    require('@jupyterlab/theme-dark-extension'),
    require('@jupyterlab/theme-light-extension'),
    require('@jupyterlab/tooltip-extension'),
    require('@jupyterlab/ui-components-extension')
  ];
  var lab = new JupyterLab();
  lab.registerPluginModules(mods);
  /* eslint-disable no-console */
  console.log('Starting app');
  await lab.start();
  console.log('App started, waiting for restore');
  await lab.restored;
  console.log('Example started!');
});

it('should be the loader used by the application', () => {
      expect(lab.loader).to.be(null);
      lab = new JupyterLab({ loader });
      expect(lab.loader).to.be(loader);
    });

it('should be the info about the application', () => {
      expect(lab.info.version).to.be('unknown');
      expect(lab.info.gitDescription).to.be('unknown');
      lab = new JupyterLab({
        version: 'foo',
        gitDescription: 'foo'
      });
      expect(lab.info.version).to.be('foo');
      expect(lab.info.gitDescription).to.be('foo');
    });

it('should accept options', () => {
      lab = new JupyterLab({
        version: 'foo',
        gitDescription: 'foo',
        loader
      });
    });

beforeEach(() => {
    lab = new JupyterLab();
  });

function createLab(loader: ModuleLoader): JupyterLab {
  const lab = new JupyterLab({
    loader,
    gitDescription: process.env.GIT_DESCRIPTION,
    namespace: 'jupyterlab',
    version: process.env.JUPYTERLAB_VERSION
  });
  lab.registerPluginModules(mods);
  return lab;
}

require('@jupyterlab/launcher-extension'),
    require('@jupyterlab/mainmenu-extension'),
    require('@jupyterlab/markdownviewer-extension'),
    require('@jupyterlab/mathjax2-extension'),
    require('@jupyterlab/notebook-extension'),
    require('@jupyterlab/rendermime-extension'),
    require('@jupyterlab/running-extension'),
    require('@jupyterlab/settingeditor-extension'),
    require('@jupyterlab/shortcuts-extension'),
    require('@jupyterlab/tabmanager-extension'),
    require('@jupyterlab/terminal-extension'),
    require('@jupyterlab/theme-dark-extension'),
    require('@jupyterlab/theme-light-extension'),
    require('@jupyterlab/tooltip-extension')
  ];
  var lab = new JupyterLab({
    name: 'JupyterLab Example',
    namespace: 'lab-example',
    version: require('./package.json').version
  });
  lab.registerPluginModules(mods);
  lab.start();
});

function createLab(loader: ModuleLoader): JupyterLab {
  const lab = new JupyterLab({
    loader,
    gitDescription: process.env.GIT_DESCRIPTION,
    namespace: 'jupyterlab',
    version: process.env.JUPYTERLAB_VERSION
  });
  lab.registerPluginModules(mods);
  return lab;
}