ArrayIndexes.md

typelab / utils / ArrayIndexes

type ArrayIndexes<T, IncludeString> = T extends ReadonlyArray ? _IfNotAnyOrNever<T, number extends T["length"] ? number : Exclude<keyof T, keyof WritableArray> extends infer IndexesString ? ParseInt<IndexesString> extends infer IndexesNumber ? IsTrue<IncludeString> extends true ? IndexesNumber | IndexesString : IndexesNumber : never : never> : never;

Extracts the index keys of an Array or Tuple type.

• For a Tuple, returns T index union.
• For a general Array, returns number since arrays are indexed by numbers.

Type Parameters

Type Parameter	Default type	Description
T	‐	The array or Tuple type to extract index keys from.
IncludeString extends boolean	false	Whether to include string keys (true) or only numeric keys (false). Defaults to false.

Returns

The keys of the Tuple (as both string and number) or number for general arrays.

Example

// 0 | 1 | 2
type Result1 = ArrayIndexes<[string, number, boolean]>;

// 0 | 1 | 2 | "0" | "1" | "2"
type Result2 = ArrayIndexes<[string, number, boolean], true>;

// number
type Result3 = ArrayIndexes<string[]>;

// never
type Never = ArrayIndexes<any>;