Optional

optional

function optional( decoder: Decoder<T> ): Decoder<T | undefined> (source)

function optional( decoder: Decoder<T>, default: V ): Decoder<T | V>

function optional( decoder: Decoder<T>, default: () => V ): Decoder<T | V>

Accepts whatever the given decoder accepts, or undefined.

If a default value is explicitly provided, return that instead in the undefined case.

optional(string).verify(input)

A typical case where optional() is useful is in decoding objects with optional fields:

object({
  id: number,
  name: string,
  address: optional(string),
});

Which will decode to type:

{
  id: number;
  name: string;
  address?: string;
}

nullable

function nullable( decoder: Decoder<T> ): Decoder<T | null> (source)

function nullable( decoder: Decoder<T>, default: V ): Decoder<T | V>

function nullable( decoder: Decoder<T>, default: () => V ): Decoder<T | V>

Accepts whatever the given decoder accepts, or null.

If a default value is explicitly provided, return that instead in the null case.

nullable(string).verify(input)

Or use it with a default value:

const decoder = nullable(isoDate, () => new Date());

decoder.verify('2022-01-01T12:00:00Z') === '2022-01-01T12:00:00Z';
decoder.verify(null); // the current date

nullish

function nullish( decoder: Decoder<T> ): Decoder<T | null | undefined> (source)

function nullish( decoder: Decoder<T>, default: V ): Decoder<T | V>

function nullish( decoder: Decoder<T>, default: () => V ): Decoder<T | V>

Accepts whatever the given decoder accepts, or null, or undefined.

If a default value is explicitly provided, return that instead in the null/undefined case.

nullish(string).verify(input)

Or use it with a default value:

const decoder = nullish(string, null);

decoder.verify('hello') === 'hello';
decoder.verify(null) === null;
decoder.verify(undefined) === null;