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Chars equal

charsEqual validates that a string has exactly a specified number of characters.

It enforces strict structural string validation and rejects any non-string value or string whose length does not match the required length. If the value is not a string or has the wrong length, the rule emits a single validation event. Otherwise, it produces no validation output.

Signature

Through the API:

.charsEqual(exact: number)

And internally:

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

Events

Event code Description
type.not.valid Value is not structurally a string
string.has.invalid-length String length does not match required length

Design rationale

  • Provides a strict, predictable exact length string validation.
  • Rejects non-string 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

charsEqual 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 string, emits type.not.valid.
  • If the value is a string but has wrong length, emits string.has.invalid-length.
  • If the value is a string with exactly the required length → returns an empty result set.

Examples

Valid string with exact length

await charsEqual(5)("hello", "$");
// → []

String with wrong length

await charsEqual(5)("hi", "$");
// → [
//     JaneEvent{
//       kind: "error",
//       code: "string.has.invalid-length",
//       path: "$",
//       ...
//     }
//   ]

Non-string value

await charsEqual(3)(42, "$");
// → [
//     JaneEvent{
//       kind: "error",
//       code: "type.not.valid",
//       path: "$",
//       ...
//     }
//   ]