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Includes

includes validates that an array contains a specific required item.

It performs a strict structural array check and rejects any non‑array value. If the value is an array and does not contain the required item (using JavaScript’s Array.prototype.includes semantics), the rule emits a single validation event. Otherwise, it produces no validation output.

Signature

Through the API:

.includes(item)

And internally:

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

Events

Event code Description
array.not.array Value is not structurally an array.
array.is.missing-value Array does not contain the required item.

Design rationale

  • Enforces strict, predictable inclusion of a specific item in an array.
  • Uses JavaScript Array.prototype.includes semantics (value equality for primitives, reference equality for objects).
  • Rejects non‑array values with a structural‑type diagnostic.
  • Emits exactly one event per failure for clarity and composability.
  • Never coerces, normalizes, or transforms — validation is explicit and opt‑in.
  • Async‑compatible and returns a readonly array of JaneEvent objects.

Invoke

includes 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 an array, emits array.not.array.
  • If the value is an array and does not include the required item, emits array.is.missing-value.
  • Otherwise, returns an empty result set.

Examples

Valid — item present

const rule = includes("x");

await rule(["a", "x", "b"], "$");
// → []

Invalid — item missing

const rule = includes(42);

await rule([1, 2, 3], "$");
// → [
//     JaneEvent{
//       kind: "error",
//       code: "array.is.missing-value",
//       path: "$",
//       ...
//     }
//   ]

Non‑array value

const rule = includes("x");

await rule("not-an-array", "$");
// → [
//     JaneEvent{
//       kind: "error",
//       code: "array.not.array",
//       path: "$",
//       ...
//     }
//   ]