MSW v2 brings the biggest API change to the library since its inception. Alongside the new API, it includes various features, such as ReadableStream support, ESM-compatibility, and countless bug fixes.

Codemod supports a mostly automated MSW v2 upgrade experience. This page provides tips and resources you may need for a successful migration.

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Getting started

MSW v2 Upgrade Guide

MSW v2 Upgrade Recipe

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Migration Steps

1

Installation

npm install msw@latest
2

Run codemods

Inside your project’s root directory, run the MSW v2 upgrade recipe:

npx codemod@latest msw/2/upgrade-recipe
3

Fix false negatives

The upgrade recipe does not change the signatures of MSW handlers, if they were called using a custom factory function, for example to provide more type-safety or else. For example, the following code will only be partially updated:

export function mockFactory<T extends MyComplexType>(
export function mockFactory<T extends MyComplexType>(
    url: string,
    resolver: MyResolverType,
) {
    return rest.get(url, resolver);
}

const handlers = [
    mockFactory('/some/url', (req, res, ctx) => {
        return res(ctx.status(200));
    }),
];

Additionally, if you were using req.body in your interceptors, this codemod will blindly assume you want await request.json() instead of any other type. You will have to correct that manually.