Custom fetch implementation

fetch-mock uses Request, Response and Headers constructors internally, and obtains these from node-fetch in Node.js, or window in the browser. If you are using an alternative implementation of fetch you will need to configure fetch-mock to use its implementations of these constructors instead. These should be set on the fetchMock.config object, e.g.

const ponyfill = require('fetch-ponyfill')();
Object.assign(fetchMock.config, {
	Headers: ponyfill.Headers,
	Request: ponyfill.Request,
	Response: ponyfill.Response,
	fetch: ponyfill,
});