Type Alias FixedLengthArray<Element, Length, ArrayPrototype>

FixedLengthArray: Pick<
    ArrayPrototype,
    Exclude<keyof ArrayPrototype, ArrayLengthMutationKeys>,
> & {
    "[iterator]": () => IterableIterator<Element>;
    length: Length;
    [index: number]: Element;
}

Create a type that represents an array of the given type and length. The array's length and the Array prototype methods that manipulate its length are excluded in the resulting type.

Please participate in this issue if you want to have a similar type built into TypeScript.

Use-cases:

  • Declaring fixed-length tuples or arrays with a large number of items.
  • Creating a range union (for example, 0 | 1 | 2 | 3 | 4 from the keys of such a type) without having to resort to recursive types.
  • Creating an array of coordinates with a static length, for example, length of 3 for a 3D vector.

Note: This type does not prevent out-of-bounds access. Prefer ReadonlyTuple unless you need mutability.

Type Parameters

Example

import type {FixedLengthArray} from 'type-fest';

type FencingTeam = FixedLengthArray<string, 3>;

const guestFencingTeam: FencingTeam = ['Josh', 'Michael', 'Robert'];

const homeFencingTeam: FencingTeam = ['George', 'John'];
//=> error TS2322: Type string[] is not assignable to type 'FencingTeam'

guestFencingTeam.push('Sam');
//=> error TS2339: Property 'push' does not exist on type 'FencingTeam'

See

ReadonlyTuple

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