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Convert a Promise

When you hold a Promise<T> from an existing API, wrap it in Result.fromPromise to get a Pending<T, E> whose rejection path is captured as Err.

Basic usage​

import { Result } from "antithrow";

const settled = await Result.fromPromise(fetch("/api"));
if (settled.isOk()) {
	use(settled.value);
}

The returned Pending is PromiseLike, so await yields a Settled<T, E>.

Typing the error​

Result.fromPromise accepts an optional mapper to shape the rejection reason:

type FetchError = { kind: "network"; cause: unknown };

const settled = await Result.fromPromise(fetch("/api"), (cause): FetchError => ({
	kind: "network",
	cause,
}));

Without the mapper, E is unknown (promises can reject with anything).

When to use this instead of Result.try​

  • Use Result.fromPromise when you already have a Promise.
  • Use Result.try with an async function when you want to defer invocation until inside antithrow's control.

Both produce a Pending; fromPromise avoids constructing an extra closure.

See also​