const client = google.accounts.oauth2.initTokenClient({

  client_id: 'YOUR_GOOGLE_CLIENT_ID',

  scope: 'https://www.googleapis.com/auth/calendar.readonly',

  callback: (tokenResponse) => {

    if (tokenResponse && tokenResponse.access_token) {

      gapi.client.setApiKey('YOUR_API_KEY');

      gapi.client.load('calendar', 'v3', listUpcomingEvents);

    }

  },

});

​

function listUpcomingEvents() {

  gapi.client.calendar.events.list(...);

}