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.

[fatso83]

Just to clarify: "the team" is essentially me most of the time, these days. And since I am usually not doing much javascript coding these days, any work on fake timers I have been doing for the last 5 years is purely voluntary work in my free time, so just providing a bunch of work on some random feature is usually not something that is likely to just happen by chance 😉

My main concerns are

1. core maintanance: refactoring inner bits for easier maintenance, etc
2. fixing bugs
3. improving performance (like the 2000x perf increase the refactoring to using heap the other day provided)

because that's what I enjoy 😊

[helloimalastair]

Of course, this has been on the back burner for me for a bit too(will take a crack at it if I get a bit of time).

My intention was definitely not to imply it as a request for you, but more a "would you be ok if this was implemented for fake-timers or no". I apologize if it came across differently.