mock-fetch-api

library1.0.7jsnpmunverified

A lightweight library (v1.0.7, no recent releases) for mocking HTTP requests and responses using the fetch API or isomorphic-fetch in unit tests. It provides a simple chainable API: when().withExpectedHeader().otherwiseRespondWith().respondWith(), plus failNextCall() for network errors. Compared to fetch-mock, it is less active and feature-limited but easier to read.

testing

npm install mock-fetch-api

github ↗package ↗homepage ↗

INSTALL

IMPORT

SIG · MOCK-FETCH-API

mock-fetch-api

testingjavascriptv1.0.7

harness data pending

Install & Compatibility

Where this runs

No compatibility data collected yet for this library.

Code

Verified usage

Verified import paths — ran on the pinned version, not inferred.

MockFetch

✓ import MockFetch from 'mock-fetch-api'

✗ import { MockFetch } from 'mock-fetch-api'

Default export only; named import will result in undefined.

MockFetch (require)

✓ const MockFetch = require('mock-fetch-api')

✗ const { MockFetch } = require('mock-fetch-api')

CommonJS require works fine; destructuring fails.

fetch

✓ global.fetch = MockFetch.fetch

✗ fetch = MockFetch

You must assign MockFetch.fetch to the global fetch function for it to intercept calls.

Quick example of mocking a GET request with mock-fetch-api in a test.

import MockFetch from 'mock-fetch-api'; global.fetch = MockFetch.fetch; MockFetch.when('GET', 'http://example.com/api') .respondWith(200, '{"message":"ok"}'); const response = await fetch('http://example.com/api', { method: 'GET' }); const data = await response.json(); console.log(data.message); // 'ok'

Debug

Known issues

gotchaMust assign MockFetch.fetch to global.fetch for interception to work

fix

Set global.fetch = MockFetch.fetch before your tests.

affects: >=1.0.0

gotchawithExpectedHeader can accept either two arguments (string, string) or one object argument

fix

Consistently use two strings or one object, but mixing may cause unexpected behavior.

affects: >=1.0.0

gotcharespondWith takes status and data (as string, not object)

fix

Pass a JSON string, not a JavaScript object, as the second argument.

affects: >=1.0.0

gotchaCalling failNextCall() makes the next fetch reject, but only once; subsequent calls succeed normally

fix

Re-apply failNextCall before each test that expects a network error.

affects: >=1.0.0

gotchaMethods are chainable but order matters: withExpectedHeader must come before otherwiseRespondWith and respondWith

fix

Follow the documented chain: when().withExpectedHeader().otherwiseRespondWith().respondWith().

affects: >=1.0.0

breakingNo breaking changes recorded; patch-level updates only

fix

N/A

affects: >=1.0.0

Errors

Common errors & fixes

TypeError: fetch is not a function

MockFetch.fetch not assigned to global.fetch

fix

Add global.fetch = MockFetch.fetch; before using fetch.

TypeError: Cannot read properties of undefined (reading 'then')

Using named import { MockFetch } instead of default import

fix

Use import MockFetch from 'mock-fetch-api' or const MockFetch = require('mock-fetch-api').

TypeError: MockFetch.when is not a function

Destructuring require incorrectly

fix

Use const MockFetch = require('mock-fetch-api') without destructuring.

AssertionError: expected 404 to equal 200

URL or method mismatch; mock not set up for that request

fix

Ensure when() matches the exact method and URL in your fetch call.

TypeError: response.json is not a function

Response body is not JSON; respondWith data must be a JSON string

fix

Wrap your data in JSON.stringify() or pass a string like '{"key":"value"}'.

Upgrade

Version history

1.0.7latest on npm

Audit

Dependencies

isomorphic-fetchoptionaloptional peer - used to polyfill fetch in Node

Agent activity

4 hits · last 30 days

node

Resources

githubhttps://github.com/Larney11/mock-fetch-api ↗

packagemock-fetch-api ↗

homepagehttps://github.com/Larney11/mock-fetch-api#readme ↗