validateMap

Validates that a value is a Map instance. This helper uses the isMap type guard internally. Only native Map instances and Map wrapper objects created via Object(...) pass this check.

It never throws and never mutates input. Use it when you need to validate key–value collections before applying further structural or element‑level validation.

Signature

function validateMap(
  value: unknown,
  field: string
): ValidationResult<Map<unknown, unknown>>

Parameters

Name	Data type	Description
value	unknown	The value to validate.
field	string	The name of the field being validated, used in error reporting.

Returns

A ValidationResult<Map<unknown, unknown>>:

• { ok: true, value: Map }: If the value is a Map.
• { ok: false, field, message }: Otherwise.

Behavior

• Uses isMap internally.
• Accepts:
• new Map().
• new Map([...]).
• Object(new Map()).
• Subclasses of Map.
• Rejects:
• Plain objects
• Arrays
• Sets, WeakMaps, WeakSets
• Primitives
• Never throws or mutates input.

Examples

validateMap(new Map([["a", 1]]), "data")
// { ok: true, value: Map { "a" => 1 } }

validateMap({}, "obj")
// { ok: false, field: "obj", message: "Value must be a Map" }

Notes

• This validator checks only that the value is a Map. It does not validate key or value types. For that, use higher‑level helpers.