API for Mocking Globals with Isolation

[helloimalastair]

Hi y'all!

I wanted to ask, what is the stance of the team on providing a way to set mocks on global timing-related APIs that can be locked to a given scope? For example:

import FakeTimers from "@sinonjs/fake-timers";

const timer = FakeTimers.install({ toFake: ['Date'] });

function blockA() {
	return timer.useSystemTime(0, () => `Current timetstamp is ${Date.now()}`);
}

function blockB() {
	return `Current timetstamp is ${Date.now()}`;
}

// Run concurrently, blockA returns timestamp of 0,
// while blockB returns actual timestamp

This is related to vitest#5750

[fatso83]

This sounds very interesting indeed, and I did go to checkout the example vitest sandbox. I only saw a "Upgrade Required" in the output, which might explain the failing test 😄 I did catch the gist of the concept though, and I absolutely find the concept of keeping async contexts worth considering.

Are there anyone outside of Node doing something similar to AsyncContext?

It would be fine to have a node-only feature to start out.

[helloimalastair]

In my case specifically, I'm writing tests for a project built on Workers, but in that case, you still have access to AsyncContext because of the platform's Node Compatibility Mode.

[fatso83]

Sure, if you can flesh out a PR or a POC we can have something to discuss.