Perform worker update in parallel

[kettanaito]

Prerequisites

• I confirm my issue is not in the opened issues
• I confirm the Frequently Asked Questions didn't contain the answer to my issue

Environment check

• I'm using the latest msw version
• I'm using Node.js version 18 or higher

Browsers

No response

Reproduction repository

Any example

Reproduction steps

1. Have a context that activates MSW.
2. Have another MSW activation in the same context.

Current behavior

When MSW finds a matching registration and attempts to reuse it, it first updates the worker. That is done to make sure that the existing worker registration is up-to-date. For example, if you are registering a worker that doesn't match the existing worker (i.e. the script has changed due to the MSW version change), the existing worker will be marked as redundant.

msw/src/browser/setupWorker/start/utils/getWorkerInstance.ts

Lines 39 to 40 in 452686d

	// When the Service Worker is registered, update it and return the reference.
	return existingRegistration.update().then(() => {

The problem is that .update() takes time. It needs to fetch the worker script, evaluate it byte-by-byte, comparing the old and the new scripts. That's a potential overhead that MSW doesn't have to await.

Expected behavior

Update is scheduled to run in the background. MSW resolves with the existing worker registration immediately.

[kettanaito]

Released: v2.4.10 🎉

This has been released in v2.4.10!

• 📄 Release notes
• 📦 npm package

Make sure to always update to the latest version (npm i msw@latest) to get the newest features and bug fixes.

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