loadable and unwrap were not updated to check for isPromiseLike and are broken in applications with zone.js

[leobastiani]

Bug Description

I saw the related discussion and pull request although I think loadable and unwrap didn't have their patch as intended
Can you have a look, please?

I know we have a solution here, but just to mention it is also possible to do const isPromise = (x) => x instanceof Promise || x instanceof (async () => {})().constructor which was what I did in my project with patch-package until now

Reproduction Link

https://stackblitz.com/edit/zonejs-loadable-jotai?file=index.js

[dai-shi]

As discussed somewhere, it's intentional. Those promises have already created with new Promise() before they reach loadable and unwrap, so my assumption was instanceof Promise should work, if non-native Promise is even used.

What promise library do you use? Can you create a very small one-file reproduction with https://stackblitz.com?
I'm happy to change the logic with typeof x.then === 'function'. But, I'll wait for the reproduction first.

[leobastiani]

Thanks for the answer and your effort.

As you can see here https://stackblitz.com/edit/zonejs-loadable-jotai?file=index.js

Promise.resolve() instanceof Promise; //  is true

but

const myPromise = (async () => {})(); // instance of the real Promise
myPromise instanceof Promise; // is false
myPromise instanceof Promise || myPromise instanceof (async () => {})().constructor; // is true

https://www.npmjs.com/package/zone.js is overriding the global Promise class and is very adopted https://www.npmjs.com/package/zone.js?activeTab=dependents

[dai-shi]

Thanks. I'm not sure how that stackblitz is configured, but I can confirm:

> (async () => {})() instanceof Promise
false

Those promises have already created with new Promise() before they reach loadable and unwrap

Now, I understand that it was only true before #2695 was introduced.
Thanks for the catch. I'll open a PR.
A question to you is if you know how to reproduce this in a unit test.

[dai-shi]

#3068

[leobastiani]

A question to you is if you know how to reproduce this in a unit test.

https://stackblitz.com/edit/jotai-discussion-3065?file=test%2Fexample.test.ts

Sorry for the delay, I was writing the example and accidentally pressed the reload shortcut, I ended up losing what I was writing hahaha

I just wrote two examples

1. it's a promise but it is not a PromiseLike
2. it's a promise but instanceof Promise is false (because the global Promise has been changed)

[dai-shi]

Thanks. The first one is an expected limitation. The second one looks good, but I'm not sure if writing a test would be easy. Can we mock globalThis? If anyone has suggestion, feel free to open a PR.