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Is date

isDate validates that a value is a valid JavaScript Date instance.

It performs a strict type check ensuring the value is a Date instance, then validates that the Date is not an "Invalid Date" (NaN timestamp). If the value is not a Date or is invalid, the rule emits a single validation event. Otherwise, it produces no validation output.

Signature

Through the API:

.isDate()

And internally:

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

Events

Event code Description
date.not.date Value is not a Date instance
date.is.invalid Date instance represents an invalid date (NaN timestamp)

Design rationale

  • Provides a strict, predictable Date instance validation.
  • First ensures the value is a Date object using instanceof Date.
  • Then validates the Date is not "Invalid Date" using isNaN(date.getTime()).
  • 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

isDate 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 Date instance, emits date.not.date.
  • If the value is a Date but invalid, emits date.is.invalid.
  • If the value is a valid Date instance → returns an empty result set.

Examples

Valid Date

await isDate(new Date("2023-01-01"), "$");
// → []

Invalid Date instance

await isDate(new Date("invalid"), "$");
// → [
//     JaneEvent{
//       kind: "error",
//       code: "date.is.invalid",
//       path: "$",
//       ...
//     }
//   ]

Non-Date value

await isDate("2023-01-01", "$");
// → [
//     JaneEvent{
//       kind: "error",
//       code: "date.not.date",
//       path: "$",
//       ...
//     }
//   ]