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optionalize

Overview​

optionalize creates a codec for an object type where properties whose codecs can resolve to undefined (typically created using optional or t.union([..., t.undefined])) are marked as optional (?) in the resulting TypeScript type.

Specification​

Accepts one argument:

  • props: (object) An object that maps property names to io-ts codecs, similar to t.type or t.partial.

Returns a new object codec. The codec effectively combines t.type (for required properties) and t.partial (for properties whose codecs include t.undefined).

Usage Example​

import * as t from 'io-ts';
import { optional, optionalize } from '@api-ts/io-ts-http';

const ItemCodec = optionalize({
  requiredId: t.string,
  optionalValue: optional(t.number), // Uses optional combinator
  maybeDefined: t.union([t.string, t.undefined]), // Also becomes optional
});

// Resulting type:
// type Item = {
//   requiredId: string;
//   optionalValue?: number;
//   maybeDefined?: string;
// }