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Is false

isFalse validates that a value is the boolean literal false.

It performs a strict boolean type check and then enforces literal equality. Any non-boolean value or the literal true results in a single validation event. Otherwise, it produces no validation output.

Signature

Through the API:

.isFalse()

And internally:

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

Events

Event code Description
boolean.not.boolean Value is not a boolean
boolean.not.false Value is boolean but not false

Design rationale

  • Provides a strict, predictable literal false validation.
  • First ensures the value is a boolean, then checks for exact false value.
  • Rejects falsy values that aren't the actual boolean false.
  • Useful for enforcing strict boolean requirements.
  • 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

isFalse 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 boolean, emits boolean.not.boolean.
  • If the value is a boolean but not false, emits boolean.not.false.
  • If the value is exactly false → returns an empty result set.

Examples

Valid literal false

await isFalse(false, "$");
// → []

Boolean true

await isFalse(true, "$");
// → [
//     JaneEvent{
//       kind: "error",
//       code: "boolean.not.false",
//       path: "$",
//       ...
//     }
//   ]

Non-boolean values

await isFalse("false", "$");
// → [
//     JaneEvent{
//       kind: "error",
//       code: "boolean.not.boolean",
//       path: "$",
//       ...
//     }
//   ]

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