All the polyfills you may need to run service-mocker.
npm i service-mocker-polyfills --save-dev
// make sure polyfill is imported first
import 'service-mocker-polyfills';
// other stuff
import { createClient } from 'service-mocker/client';
import 'service-mocker-polyfills/promise';
import 'service-mocker-polyfills/fetch';
import 'service-mocker-polyfills/url';