Quickstart

Setting up your mock

• The commonest use case is fetchMock.mock(matcher, response), where matcher is an exact url or regex to match, and response is a status code, string or object literal.
• You can also use fetchMock.once() to limit to a single call or fetchMock.get(), fetchMock.post() etc. to limit to a method.
• All these methods are chainable so you can easily define several mocks in a single test.

fetchMock
	.get('http://good.com/', 200)
	.post('http://good.com/', 400)
	.get(/bad\.com/, 500);

Analysing calls to your mock

• fetchMock.called(matcher) reports if any calls matched your mock (or leave matcher out if you just want to check fetch was called at all).
• fetchMock.lastCall(), fetchMock.lastUrl() or fetchMock.lastOptions() give you access to the parameters last passed in to fetch.
• fetchMock.done() will tell you if fetch was called the expected number of times.

Tearing down your mock

• fetchMock.resetHistory() resets the call history.
• fetchMock.reset() or fetchMock.restore() will also restore fetch() to its native implementation

Example

Example with Node.js: suppose we have a file make-request.js with a function that calls fetch:

module.exports = function makeRequest() {
	return fetch('http://httpbin.org/my-url', {
		headers: {
			user: 'me',
		},
	}).then(function (response) {
		return response.json();
	});
};

We can use fetch-mock to mock fetch. In mocked.js:

var makeRequest = require('./make-request');
var fetchMock = require('fetch-mock');

// Mock the fetch() global to return a response
fetchMock.get(
	'http://httpbin.org/my-url',
	{ hello: 'world' },
	{
		delay: 1000, // fake a slow network
		headers: {
			user: 'me', // only match requests with certain headers
		},
	},
);

makeRequest().then(function (data) {
	console.log('got data', data);
});

// Unmock.
fetchMock.reset();

Result:

$ node mocked.js
'got data' { hello: 'world' }