Interop with native promises

fromEager⁠#

This function converts an async function to a LazyPromise, and supports the AbortController API:

// Type inferred as LazyPromise<string>
const lazyPromise = fromEager(async ({ signal }) => {
  const response = await fetch("https://example.com", { signal });
  return response.text();
});

If the subscription is disposed before the returned promise settles, the signal is aborted with an AbortError. The abort controller is created lazily, so there’s no cost if the callback does not read the signal property of the object passed to it. The callback can also be a regular (non-async) function, and any non-Promise values it returns are passed on synchronously.

toEager⁠#

This is a method that converts a LazyPromise to a Promise, and it too supports AbortController.

const controller = new AbortController();

// `signal` is optional.
const promise = lazyPromise.toEager({ signal: controller.signal });

// Disposes the subscription and rejects `promise` with
// `controller.signal.reason`.
controller.abort();