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Has key

hasKey validates that a plain object contains a specific required own enumerable key.

It performs a strict structural check ensuring the value is a plain object, then validates that the specified key exists as an own property. If the value is not a plain object or is missing the required key, the rule emits a single validation event. Otherwise, it produces no validation output.

Signature

Through the API:

.hasKey(requiredKey: string)

And internally:

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

Events

Event code Description
object.not.plain-object Value is not a JSON-compatible plain object
object.has.missing-key Object does not contain the required key

Design rationale

  • Provides a strict, predictable required key validation.
  • First ensures the value is a plain object, then checks for key presence.
  • Uses Object.prototype.hasOwnProperty.call() for reliable own property detection.
  • 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

hasKey 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 plain object, emits object.not.plain-object.
  • If the value is a plain object but missing the required key, emits object.has.missing-key.
  • If the value is a plain object containing the required key → returns an empty result set.

Examples

Valid object with required key

await hasKey("name")({ name: "John", age: 30 }, "$");
// → []

Object missing required key

await hasKey("name")({ age: 30 }, "$");
// → [
//     JaneEvent{
//       kind: "error",
//       code: "object.has.missing-key",
//       path: "$",
//       ...
//     }
//   ]

Array (invalid)

await hasKey("name")([1, 2, 3], "$");
// → [
//     JaneEvent{
//       kind: "error",
//       code: "object.not.plain-object",
//       path: "$",
//       ...
//     }
//   ]