読み込み専用な[[配列型 (TypeScript)|配列型]]。
```ts
const writable: Array<string> = ["a", "i", "u"];
writable[0] = "hoge"
const readonlyArray: ReadonlyArray<string> = ["a", "i", "u"];
readonlyArray[0] = "hoge"
// Index signature in type 'readonly string[]' only permits reading.(2542)
```
<button class="playground"><a href="https://www.typescriptlang.org/play?#code/MYewdgzgLgBA7gJwJZQIYCMA2BTAXDAQQQVQE8AeaZMAcwD4YBeGAbQCJU2AaGNpb3gFc2AXQDcAKEQoMOFgAYRTXgAsQNbG0kTQkWAmyoAJuEykiJUvgBKhk2DMWylKNXrL2nHnwFth4iQNjU3NiMgUlZjY1DS0JAHp4mABJMCNsAA8YCCQaMFQoQQMYJDAYKFIAB2wYAHIg+zNs11KaFhFamBCYaoQAWxQIGAbWgDoACgAmAFYAFkmASgkgA">Playground</a></button>
以下の糖衣構文でもOK。
```ts
const readonlyArray: readonly string[] = ["a", "i", "u"]
```
## MOC
- 📒**関連**
- [[ReadonlyArrayはreadonlyプロパティのように双方向代入はできない]]
- 📜**アクティビティ**
- 📝**トラブルシューティング**