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Negative

negative validates that a number is strictly less than zero.

It enforces strict numeric validation and rejects any non-number value, NaN, or non-negative numbers. If the value is not a number or is not negative, the rule emits a single validation event. Otherwise, it produces no validation output.

Signature

Through the API:

.negative()

And internally:

export const negative: ValidationRule
(value: unknown, path: FieldPath) => Promise<ReadonlyArray<JaneEvent>>

Events

Event code Description
type.not.valid Value is not structurally a number or is NaN
number.not.negative Number is not strictly less than zero

Design rationale

  • Provides a strict, predictable negative number validation.
  • Rejects zero and positive values explicitly.
  • Rejects non-number values with a clear structural-type diagnostic.
  • Never coerces or normalizes — validation is explicit and opt-in.
  • Emits exactly one event per failure for clarity and composability.
  • Async-compatible and returns a readonly array of JaneEvent objects.

Invoke

negative runs only when explicitly included in a boundary or pipeline. It does not run automatically.

The rule activates when:

  • The value is any JavaScript value.
  • If the value is not a number or is NaN, emits type.not.valid.
  • If the value is a number but not less than zero, emits number.not.negative.
  • If the value is a negative number → returns an empty result set.

Examples

Valid negative number

await negative(-5, "$");
// → []

Zero

await negative(0, "$");
// → [
//     JaneEvent{
//       kind: "error",
//       code: "number.not.negative",
//       path: "$",
//       ...
//     }
//   ]

Non-number value

await negative("-5", "$");
// → [
//     JaneEvent{
//       kind: "error",
//       code: "type.not.valid",
//       path: "$",
//       ...
//     }
//   ]