is-actual-promise

Similar to p-is-promise and is-promise, which are also both fine alternatives to this.

Differences (ie, "why this thing then?")

• This module is hybrid, so it can be used in either commonjs or esm. is-promise is hybrid, but p-is-promise is ESM-only.
• This module asserts that the tested value supplies the full actual Promise interface, not just PromiseLike (ie, it also asserts .catch() and .finally(). (p-is-promise tests for .catch(), neither tests for .finally().)
• This module provides a named export rather than a default export, which is a bit less of a hassle in some scenarios.
• This module does not verify the resolution type of the Promise, since that cannot be determined or verified, only that it's a Promise<any | void>.

(Note that this module does not verify that the .catch(), .then(), and .finally() methods return Promises, because that is impossible at run-time without actually calling them. No duck-typing method should ever be considered fully authoritative.)

USAGE

import { isPromise } from 'is-actual-promise'

console.log(isPromise(new Promise(() => {}))) // true
console.log(isPromise((async () => true)())) // true
console.log(isPromise(Promise.resolve(true))) // true
console.log(isPromise({
  then: async () => 5,
  finally: async () => {},
  catch: () => {},
})) // true, but not accurate, limitation of duck typing