filterOrElse

function ResultAsync.filterOrElse(
    result: AwaitableResult<T, E>,
    predicate: (value: T) => boolean,
    orElse: (value: T) => F | Promise<F>
): ResultAsync<T, E | F>

Filters the Ok value using the predicate function. If the result is Ok and the predicate returns true, returns the original result. If the predicate returns false, calls orElse with the Ok value and returns an Err with the result. If the result is already an Err, returns it unchanged.

Can be used for type narrowing.

Example

data-first

await ResultAsync.filterOrElse(
    ok(5),
    (x) => x > 3,
    (x) => `${x} is too small`,
);
// Ok<number>(5)

await ResultAsync.filterOrElse(
    ok(1),
    (x) => x > 3,
    (x) => `${x} is too small`,
);
// Err<string>("1 is too small")

await ResultAsync.filterOrElse(
    err("fail"),
    (x) => x > 3,
    (x) => `${x} is too small`,
);
// Err<string>("fail")

data-last

await pipe(
    ok(1),
    ResultAsync.filterOrElse(
        (x) => x > 3,
        (x) => `${x} is too small`,
    ),
);
// Err<string>("1 is too small")