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requiredTrue()

Requires exactly true. Every other value fails, including false, null, undefined, 1, and 'true'.

Signatures​

requiredTrue
requiredTrue(message)
requiredTrue(options)

Pass the function directly for its default behavior:

const checkout = form({
  acceptedTerms: field(false, [requiredTrue]),
});

A failure has the shape { kind: 'requiredTrue', message }. The field retains its declared value type; successful validation does not narrow nullable types.

Custom messages and errors​

const checkout = form({
  acceptedTerms: field(false, [requiredTrue('Accept the terms to continue.')]),
});

The default message is This field must be accepted.. The options object also accepts message: () => translations().requiredTrue. Returning undefined from a message function continues through node, provider, global, and built-in fallbacks. Message catalogs use the requiredTrue key. See validator messages.

An error option can replace the default error with one error, an array, or a reactive context callback. Returning null, undefined, or an empty array suppresses the failure. error and message are mutually exclusive. See custom errors.

Conditional validation​

const enabled = signal(true);
const checkout = form({
  acceptedTerms: field(false, [requiredTrue({ when: () => enabled() })]),
});

Signals read by when, messages, and custom error callbacks are tracked. An inactive rule contributes no errors or metadata. Disabled, readonly, and hidden nodes skip validation.

Required state and controls​

An active rule contributes required() === true even when its value is valid or the node is disabled. Custom error replacements retain this metadata. [formNode] mirrors the constraint to native checkbox required; optional syncInputs does the same for custom controls exposing a public checked input. Other controls receive the usual logical required state.

For a yes/no question where either answer is valid, use required with an initial null. For an existing equalTo(true) rule, requiredTrue additionally supplies acceptance metadata and its own error kind.

See the comparison and executable example and built-in validator catalog.

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