validatePlainObject

Checks whether a value is a plain object. This helper uses the isPlainObject type guard internally.

A plain object is one created via an object literal ({}) or new Object(), where the prototype is exactly Object.prototype.

Objects with a null prototype, custom prototypes, or specialized built-in types do not pass this check.

It never throws and never mutates input. Use it when you need to ensure that a value is a simple, prototype-standard object before applying further structural or key-level validation.

Signature

function validatePlainObject(
  value: unknown,
  field: string
): ValidationResult<object>

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

One of:

• { ok: true, value: object }: If the value is a plain object whose prototype is exactly Object.prototype.
• { ok: false, field: string, message: string }: If value is not a plain object.

Behavior

• Uses isPlainObject internally.
• Accepts only objects whose prototype is exactly Object.prototype.
• Accepts:
• Object literals ({})
• Objects created with new Object()
• Rejects:
• null
• Arrays
• Object.create(null)
• Functions
• Built-in objects (Map, Set, Date, RegExp).
• Class instances.
• All primitive values
• Performs no coercion.
• Never throws or mutates input.

Examples

validatePlainObject({ a: 1 }, "data")
// { ok: true, value: { a: 1 } }

validatePlainObject(new Object(), "obj")
// { ok: true, value: {} }

validatePlainObject(Object.create(null), "nullProto")
// { ok: false, field: "nullProto", message: "Value must be a plain object" }

validatePlainObject([], "arr")
// { ok: false, field: "arr", message: "Value must be a plain object" }

Notes

• This validator is stricter than validateObject, which accepts any non-null object.
• Use this validator when validating:
• JSON-like data structures
• Configuration objects
• Schema-controlled payloads
• The validator never throws and never mutates input. All error reporting goes through structured ValidationResult objects.