[API reference](https://evolu.dev/docs/api-reference) › [@evolu/common](https://evolu.dev/docs/api-reference/common) › [Array](https://evolu.dev/docs/api-reference/common/Array) › createMutableArray

```ts
function createMutableArray<T>(length: number): T[];
```

Defined in: [packages/common/src/Array.ts:201](https://github.com/evoluhq/evolu/blob/ca15b4661c40fedb9f47434497086039cbdea38e/packages/common/src/Array.ts#L201)

Creates a mutable sparse Array with the specified length.

Use it to build an Array with indexed writes when its final length is known.
Assign every index before exposing the completed Array as readonly.

### Example

```ts

const values = createMutableArray<number>(3);

for (let index = 0; index < values.length; index++) {
  values[index] = index * 10;
}

expect(values).toEqual([0, 10, 20]);
expectTypeOf(values).toEqualTypeOf<Array<number>>();
```