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Max length

maxLength validates that a string contains at most a specified maximum number of characters.

It enforces strict structural string validation and rejects any non-string value or string whose length exceeds the configured maximum. If the value is not a string or is too long, the rule emits a single validation event. Otherwise, it produces no validation output.

Signature

Through the API:

.maxLength(max: number)

And internally:

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

Events

Event code Description
type.not.valid Value is not structurally a string
string.too.long String length exceeds the maximum threshold

Design rationale

  • Provides a strict, predictable string length 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

maxLength 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 longer than the maximum, emits string.too.long.
  • If the value is a string of acceptable length → returns an empty result set.

Examples

Valid string within maximum length

await maxLength(10)("hello", "$");
// → []

String too long

await maxLength(3)("hello world", "$");
// → [
//     JaneEvent{
//       kind: "error",
//       code: "string.too.long",
//       path: "$",
//       ...
//     }
//   ]

Non-string value

await maxLength(5)(42, "$");
// → [
//     JaneEvent{
//       kind: "error",
//       code: "type.not.valid",
//       path: "$",
//       ...
//     }
//   ]