promiseToFuture

Converts a Promise to a folktale Future.

This feature is experimental!

This API is still experimental, so it may change or be removed in future versions. You should not rely on it for production applications.

Signature

promiseToFuture(aPromise)

Type(what is this?)

forall e, v:
  (Promise v e) => Future e v

Documentation

Converts a Promise to a folktale Future.

Note that this conversion may not be as accurate due to the differences in Promise and Future semantics. In particular, Promises recursively flatten any object with a .then method, and do not have a separate representation for cancellations.

If a Promise contains a rejection with Folktale's special Cancelled() value, then the resulting Future will be a cancelled Future rather than a rejected one.

Example:

const promiseToFuture = require('folktale/conversions/promise-to-future');

promiseToFuture(Promise.resolve(1));
// => Future.resolve(1)

promiseToFuture(Promise.reject(1));
// => Future.reject(1)

Properties

Source Code

Defined in source/conversions/promise-to-future.js at line 19, column 0

(aPromise) => {
  const deferred = new Deferred();
  aPromise.then(
    (value) => deferred.resolve(value),
    (error) => {
      if (Cancelled.hasInstance(error)) {
        deferred.cancel();
      } else {
        deferred.reject(error);
      }
    }
  );
  return deferred.future();
}