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fix: correct isPromise implementation #13314

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merged 7 commits into from Sep 23, 2022
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SimenB
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@SimenB SimenB commented Sep 23, 2022

Summary

The linked SO post says not to use it 馃檲

Test plan

Green CI

const isPromise = (candidate: unknown): candidate is PromiseLike<unknown> =>
candidate != null &&
(typeof candidate === 'object' || typeof candidate === 'function') &&
typeof (candidate as any).then === 'function';
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Perhaps? Just to avoid any? Or the point is to be explicit that this is still any?

Suggested change
typeof (candidate as any).then === 'function';
typeof (candidate as PromiseLike<unknown>).then === 'function';

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the cast would lie - I just want to be able to access a prop. I guess as Record<string, unknown> | (...args: unknown[]) => unknown or something is more precise looking at the typeof checks. But not really, as typeof new Map === 'object'. Just saying any seems cleanest

@@ -23,3 +23,12 @@ test('a resolved Promise', () => {
test('a rejected Promise', () => {
expect(isPromise(Promise.reject().catch(() => {}))).toBe(true);
});

test('a thenable', () => {
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this test fails with the old implementation, fwiw

@SimenB SimenB merged commit 2e608c1 into jestjs:main Sep 23, 2022
@SimenB SimenB deleted the fix-is-promise branch September 23, 2022 13:34
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3 participants