validateKeyOf

Validates that a value is a key of a given object or enum.

This helper checks whether a provided value (string or number) exists as an own property key in a target object or TypeScript enum. It never mutates input and never throws.

It uses the isKeyOf type guard internally to ensure strict, predictable behavior.

Signature

function validateKeyOf<T extends Record<PropertyKey, unknown>>(
  key: unknown,
  obj: T
): keyof T | null

Parameters

Name	Data type	Description
value	unknown	The value to validate.
object	T	The enum or object who values are valid.

Returns

One of:

• The original key if it exists in the object (keyof T).
• null: If the key is invalid.

Behavior

• Accepts string or number keys.
• Rejects any other types (boolean, null, undefined, objects, arrays).
• Works with both plain objects and enums.
• Never throws and never mutates input.

Examples

const obj = { a: 1, b: 2 };

validateKeyOf("a", obj) // "a"
validateKeyOf("b", obj) // "b"
validateKeyOf("c", obj) // null
validateKeyOf(0, obj)   // null

enum Colors { Red = "RED", Blue = "BLUE" }

validateKeyOf("Red", Colors)   // "Red"
validateKeyOf("Green", Colors) // null

Notes

• This helper validates keys, not values.
• Use validateValueOf if you want to validate enum values instead of keys.
• Ideal for configuration validation, safe property access, and schema enforcement.