mapErr

function ResultAsync.mapErr(
    result: AwaitableResult<T, E>,
    transform: (error: E) => F | Promise<F>
): ResultAsync<T, F>

Transforms the Err value using the transform function. If the result is an Err, applies the transform function to the error value and returns a new Err. If the result is Ok, returns it unchanged.

Example

data-first

await ResultAsync.mapErr(err("fail"), (e) => `Error: ${e}`);
// Err<string>("Error: fail")

await ResultAsync.mapErr(ok(5), (e) => `Error: ${e}`);
// Ok<number>(5)

data-last

await pipe(
    err("fail"),
    ResultAsync.mapErr((e) => `Error: ${e}`),
);
// Err<string>("Error: fail")