node_modules/cross-fetch/dist/node-polyfill.js

var fetchNode = require('./node-ponyfill');
var fetch = fetchNode.fetch.bind({});

fetch.polyfill = true;

if (!global.fetch) {
  global.fetch = fetch;
  global.Response = fetchNode.Response;
  global.Headers = fetchNode.Headers;
  global.Request = fetchNode.Request;
}