Function optional

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

Decoder that makes a field optional.

Type Parameters

T

Parameters

decoder: Decoder<T>
The decoder for the field when it is present

Returns Decoder<undefined | T>

A decoder that accepts either the decoded value or undefined

Example

interface User {
  name: string;
  age?: number;
}

const userDecoder = JsonDecoder.object<User>(
  {
    name: JsonDecoder.string(),
    age: JsonDecoder.optional(JsonDecoder.number())
  },
  'User'
);

userDecoder.decode({name: 'John'}); // Ok<User>
userDecoder.decode({name: 'John', age: 30}); // Ok<User>