optional

Allows undefined while keeping a strict parser for the present value. DDataParser.optional(inner) returns the output of inner when a value is provided and lets undefined pass otherwise.

Interactive example

Parameters

• inner: parser applied when a value is provided.
• coalescingValue: (optional) replaces undefined with a default value and narrows the output type to Output<inner>.
• checkers: checkerRefine or custom helpers evaluating Output<inner> | undefined.
• errorMessage: message used when the input is neither undefined nor valid for inner.

Return value

A DataParserOptional. schema.parse(data) returns DEither.success<Output | undefined> or DEither.error<DataParserError> with the incriminated path. Checkers/restrictions apply only when the value is not undefined (unless you implement different logic in your refinements).

Other examples

Extended mode

See also

• nullable - Allows accepting null in a parser
• array - Parser for arrays