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LOGOMock Service Worker
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  1. Basics
  2. Response resolver

Response resolver

Response resolver is a function that accepts a captured request and may return a mocked response.

Parameters

Response resolver function accepts the following parameters:

Parameter nameDescription
requestInformation about the captured request.
responseFunction to create the mocked response.
contextContext utilities specific to the current request handler.

Examples

Basic

The most common usage is when a response resolver is used as an argument to a request handler to specify a mocked response it should return.

1// src/mocks.js
2import { setupWorker, rest } from 'msw'
3

4const worker = setupWorker(
5  rest.get(
6    '/user',
7    // Example of a response resolver that returns
8    // a "Content-Type: application/json" response.
9    (req, res, ctx) => {
10      return res(
11        ctx.json({
12          firstName: 'John',
13          age: 38,
14        }),
15      )
16    },
17  ),
18)
19

20worker.start()

Reusable resolver

Since response resolver is a regular function, you can declare and reuse it across multiple request handlers.

1// src/mocks/resolvers/mockUser.js
2export const mockUser = (req, res, ctx) => {
3  return res(
4    ctx.json({
5      firstName: 'John',
6      age: 38,
7    }),
8  )
9}
1// src/mocks/index.js
2import { setupWorker, rest } from 'msw'
3import { mockUser } from './resolvers/mockUser'
4

5const worker = setupWorker(
6  rest.get('/user', mockUser),
7  rest.get('/me', mockUser),
8)
9

10worker.start()

Conditional response

When a response resolver returns the req.passthrough call, MSW will perform the captured request as-is, hitting the actual endpoint and returning its response. Leverage this behavior to perform conditional mocking, for example based on the request's payload.

1rest.get('/user', (req, res, ctx) => {
2  const userId = req.url.searchParams.get('userId')
3

4  if (userId === 'abc-123') {
5    // Return a mocked response only if the `userId` query parameter
6    // equals to a specific value.
7    return res(
8      ctx.json({
9        firstName: 'John',
10        lastName: 'Maverick',
11      }),
12    )
13  }
14

15  // Otherwise, explicitly state that you wish to perform this request as-is.
16  return req.passthrough()
17})

Alternatively, you can use an explicit return statement without the res() call to achieve the same behavior.

1rest.post('/login', async (req, res, ctx) => {
2  const { username } = await req.json()
3

4  if (username === 'real-user') {
5    // Bypass this request, returning an actual response
6    // only when the `username` equals to a specific value.
7    return req.passthrough()
8  }
9

10  // Otherwise, always respond with a mocked response.
11  return res(
12    ctx.json({
13      id: 'abc-123',
14    }),
15  )
16})