Use PromiseLike<T> intead of Promise<T>. Fixes #39

[rkatic]

No description provided.

[rollingversions]

Change Log for is-promise (3.0.0 → 4.0.0)

Breaking Changes

• Use PromiseLike instead of Promise in TypeScript

  This is only a breaking change for TypeScript users.

  In the following code:

  function foo(x: PromiseLike<string> | string) {
    if (isPromise(x)) {
      return x;
    } else {
      return Promise.resolve(x);
    }
  }

  TypeScript would previously have incorrectly inferred foo as returning Promise<string> when in fact it returns PromiseLike<string>. The latest version fixes this. If you instead had the following code, it should work exactly the same as before:

  function foo(x: Promise<string> | string) {
    if (isPromise(x)) {
      return x;
    } else {
      return Promise.resolve(x);
    }
  }

  This update is to reflect the fact that is-promise does "duck" typing, rather than an instanceof check.

Edit changelog

[rkatic]

Be aware that this is likely a braking change for TS users.
If, after testing a thenable, the object is used as a real promise (for example using other methods than then) without Promise.resolve it first, TS will start to fail with error(s).

[ForbesLindesay]

Thanks, this will shortly be released as 4.0.0