npmpackage.info

msw

Industry standard API mocking for JavaScript.

2.6.6

16,003

MIT

TypeScript

345,794,564 4

Installations

npm install msw

Pull Requests

Open

16

Total

845

Closed

139

Merged

690

Issues

Open

40

Total

1,090

Closed

1,050

Releases

208

v2.6.6

Published on 22 Nov 2024

v2.6.5

Published on 16 Nov 2024

v2.6.4

Published on 10 Nov 2024

v2.6.3

Published on 10 Nov 2024

v2.6.2

Published on 07 Nov 2024

v2.6.1

Published on 06 Nov 2024

View all 208 releases

Developer

mswjs

Developer Guide

BETA

Module System

CommonJS, ESM

Min. Node Version

>=18

Typescript Support

Yes

Node Version

18.20.5

NPM Version

10.8.2 Statistics

16,003 Stars

1,581 Commits

525 Forks

63 Watching

21 Branches

159 Contributors

Updated on 27 Nov 2024

Languages

TypeScript (96%)

JavaScript (3.59%)

HTML (0.3%)

Shell (0.11%)

Total Downloads

Cumulative downloads

Total Downloads

345,794,564

Last day

-0.9%

803,549

Compared to previous day

Last week

4,133,800

Compared to previous week

Last month

14.7%

17,128,942

Compared to previous month

Last year

37%

155,087,380

Compared to previous year

Daily Downloads

Weekly Downloads

Monthly Downloads

Yearly Downloads

Dependencies

@bundled-es-modules/cookie @bundled-es-modules/statuses @bundled-es-modules/tough-cookie @inquirer/confirm @mswjs/interceptors @open-draft/deferred-promise @open-draft/until @types/cookie @types/statuses chalk graphql headers-polyfill is-node-process outvariant path-to-regexp strict-event-emitter type-fest yargs

Peer Dependencies

typescript

Dev Dependencies

Versions

MSW 2.0 is finally here! 🎉 Read the Release notes and please follow the Migration guidelines to upgrade. If you're having any questions while upgrading, please reach out in our Discord server.

We've also recorded the most comprehensive introduction to MSW ever. Learn how to mock APIs like a pro in our official video course:

Mock Service Worker

Mock Service Worker (MSW) is a seamless REST/GraphQL API mocking library for browser and Node.js.

Features

Seamless. A dedicated layer of requests interception at your disposal. Keep your application's code and tests unaware of whether something is mocked or not.
Deviation-free. Request the same production resources and test the actual behavior of your app. Augment an existing API, or design it as you go when there is none.
Familiar & Powerful. Use Express-like routing syntax to intercept requests. Use parameters, wildcards, and regular expressions to match requests, and respond with necessary status codes, headers, cookies, delays, or completely custom resolvers.

"I found MSW and was thrilled that not only could I still see the mocked responses in my DevTools, but that the mocks didn't have to be written in a Service Worker and could instead live alongside the rest of my app. This made it silly easy to adopt. The fact that I can use it for testing as well makes MSW a huge productivity booster."

– Kent C. Dodds

Documentation

This README will give you a brief overview on the library but there's no better place to start with Mock Service Worker than its official documentation.

Examples

See the list of Usage examples

Browser

How does it work?

In-browser usage is what sets Mock Service Worker apart from other tools. Utilizing the Service Worker API, which can intercept requests for the purpose of caching, Mock Service Worker responds to intercepted requests with your mock definition on the network level. This way your application knows nothing about the mocking.

Take a look at this quick presentation on how Mock Service Worker functions in a browser:

How is it different?

This library intercepts requests on the network level, which means after they have been performed and "left" your application. As a result, the entirety of your code runs, giving you more confidence when mocking;
Imagine your application as a box. Every API mocking library out there opens your box and removes the part that does the request, placing a blackbox in its stead. Mock Service Worker leaves your box intact, 1-1 as it is in production. Instead, MSW lives in a separate box next to yours;
No more stubbing of fetch, axios, react-query, you-name-it;
You can reuse the same mock definition for the unit, integration, and E2E testing. Did we mention local development and debugging? Yep. All running against the same network description without the need for adapters of bloated configurations.

Usage example

1// src/mocks.js
2// 1. Import the library.
3import { http, HttpResponse } from 'msw'
4import { setupWorker } from 'msw/browser'
5
6// 2. Describe network behavior with request handlers.
7const worker = setupWorker(
8  http.get('https://github.com/octocat', ({ request, params, cookies }) => {
9    return HttpResponse.json(
10      {
11        message: 'Mocked response',
12      },
13      {
14        status: 202,
15        statusText: 'Mocked status',
16      },
17    )
18  }),
19)
20
21// 3. Start request interception by starting the Service Worker.
22await worker.start()

Performing a GET https://github.com/octocat request in your application will result into a mocked response that you can inspect in your browser's "Network" tab:

Chrome DevTools Network screenshot with the request mocked

Tip: Did you know that although Service Worker runs in a separate thread, your mock definition executes entirely on the client? This way you can use the same languages, like TypeScript, third-party libraries, and internal logic to create the mocks you need.

Node.js

How does it work?

There's no such thing as Service Workers in Node.js. Instead, MSW implements a low-level interception algorithm that can utilize the very same request handlers you have for the browser. This blends the boundary between environments, allowing you to focus on your network behaviors.

How is it different?

Does not stub fetch, axios, etc. As a result, your tests know nothing about mocking;
You can reuse the same request handlers for local development and debugging, as well as for testing. Truly a single source of truth for your network behavior across all environments and all tools.

Usage example

Take a look at the example of an integration test in Vitest that uses React Testing Library and Mock Service Worker:

1// test/Dashboard.test.js
2
3import React from 'react'
4import { http, HttpResponse } from 'msw'
5import { setupServer } from 'msw/node'
6import { render, screen, waitFor } from '@testing-library/react'
7import Dashboard from '../src/components/Dashboard'
8
9const server = setupServer(
10  // Describe network behavior with request handlers.
11  // Tip: move the handlers into their own module and
12  // import it across your browser and Node.js setups!
13  http.get('/posts', ({ request, params, cookies }) => {
14    return HttpResponse.json([
15      {
16        id: 'f8dd058f-9006-4174-8d49-e3086bc39c21',
17        title: `Avoid Nesting When You're Testing`,
18      },
19      {
20        id: '8ac96078-6434-4959-80ed-cc834e7fef61',
21        title: `How I Built A Modern Website In 2021`,
22      },
23    ])
24  }),
25)
26
27// Enable request interception.
28beforeAll(() => server.listen())
29
30// Reset handlers so that each test could alter them
31// without affecting other, unrelated tests.
32afterEach(() => server.resetHandlers())
33
34// Don't forget to clean up afterwards.
35afterAll(() => server.close())
36
37it('displays the list of recent posts', async () => {
38  render(<Dashboard />)
39
40  // 🕗 Wait for the posts request to be finished.
41  await waitFor(() => {
42    expect(
43      screen.getByLabelText('Fetching latest posts...'),
44    ).not.toBeInTheDocument()
45  })
46
47  // ✅ Assert that the correct posts have loaded.
48  expect(
49    screen.getByRole('link', { name: /Avoid Nesting When You're Testing/ }),
50  ).toBeVisible()
51
52  expect(
53    screen.getByRole('link', { name: /How I Built A Modern Website In 2021/ }),
54  ).toBeVisible()
55})

Don't get overwhelmed! We've prepared a step-by-step Getting started tutorial that you can follow to learn how to integrate Mock Service Worker into your project.

Despite the API being called setupServer, there are no actual servers involved! The name was chosen for familiarity, and the API was designed to resemble operating with an actual server.

Awards & Mentions

We've been extremely humbled to receive awards and mentions from the community for all the innovation and reach Mock Service Worker brings to the JavaScript ecosystem.

Solution Worth Pursuing

Technology Radar (2020–2021)

The Most Exciting Use of Technology

Open Source Awards (2020)

No vulnerabilities found.

10

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10

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2

Code-Review

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0

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Reason

dependency not pinned by hash detected -- score normalized to 0

Details

Info: Possibly incomplete results: error parsing shell code: invalid parameter name: .github/workflows/typescript-nightly.yml:62
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0

Fuzzing

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0

Security-Policy

Determines if the project has published a security policy.

0

SAST

Determines if the project uses static code analysis.

0

Vulnerabilities

Determines if the project has open, known unfixed vulnerabilities.

Score

4

/10

Last Scanned on 2024-11-18

The Open Source Security Foundation is a cross-industry collaboration to improve the security of open source software (OSS). The Scorecard provides security health metrics for open source projects.

Learn More

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msw

Installations

Pull Requests

16

845

139

690

Issues

40

1,090

1,050

Releases

Developer

Developer Guide

CommonJS, ESM

>=18

Yes

18.20.5

10.8.2

Statistics

Languages

Total Downloads

345,794,564

Daily Downloads

Weekly Downloads

Monthly Downloads

Yearly Downloads

Dependencies

Peer Dependencies

Dev Dependencies

Mock Service Worker

Features

Documentation

Examples

Browser

How does it work?

How is it different?

Usage example

Node.js

How does it work?

How is it different?

Usage example

Sponsors

Golden Sponsors

Silver Sponsors

Bronze Sponsors

Awards & Mentions

Solution Worth Pursuing

The Most Exciting Use of Technology

10

10

10

10

2

0

0

0

0

0

0

0

4

/10

Other packages similar to msw