Mock Service Worker

The msw (mock service worker) package is useful in intercepting and mocking requests in the browser. Its use of service workers means requests still appear in the network tab, creating a realistic mocking environment. With @graphql-mocks/network-msw the requests and responses can be handled by msw with a GraphQL handler for full GraphQL mocking in the browser.

Note: msw also provides its own method of GraphQL mocking where a named query is responded to with hardcoded fixture data. graphql-mocks provides a more universal mocking experience using resolvers and the GraphQL schema to reflect how real GraphQL APIs recursively resolve data.


Install the msw and @graphql-mocks/network-msw npm packages.

# npm
npm install --save-dev msw @graphql-mocks/network-msw
# yarn
yarn add --dev msw @graphql-mocks/network-msw


Setup msw using the REST API Documentation.

Then integreate with the graphql-mocks by creating or importing a GraphQLHandler instance and passing it to the mswResolver handler.

// src/mocks/handlers.js
import { GraphQLHandler } from 'graphql-mocks';
import { mswResolver } from '@graphql-mocks/network-msw';
import { rest } from 'msw'
import graphqlSchema from './graphql-schema';
const graphqlHandler = new GraphQLHandler({ dependencies: { graphqlSchema }});
export const handlers = ['/graphql', mswResolver(graphqlHandler))

Alternatively, instead of /graphql, a full path url can be used also. See the msw documentation for options on specifying the path of the request handler.

Next, follow the msw browser integration documentation to integrate msw properly with your front-end build.

Note: The handler src/mocks/handlers.js file created above should be imported and used with the setupWorkers function as described in the browser integration documentation.

With everything integrated, requests in the browser should be intercepted by msw and use the rest handler with the GraphQLHandler for resolving GraphQL queries.

// fetch using the url specified in src/mocks/handlers.js
// `/graphql` becomes `http://localhost/graphql`
fetch('http://localhost/graphql, {
method: 'POST',
body: JSON.stringify({
// required
query: `
query {
# graphql query
// optional
variables: {},
// optional
operationName: 'OperationName'
}).then(async (response) => {
// get the final json payload
const result = await response.json();
return result;

See the GraphQL docs for details on these body parameters, and making http requests.

Resolver Context

When using the @graphql-mocks/network-msw network handler each resolver context has an msw property which contains the req (request), res (response), and ctx (msw context), from the msw rest request handler.

function resolver(parent, args, context, info) {
const { msw } = context;
// request, response and context from the `msw` request handler
const { req, res, ctx } = msw;