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

```ts
function isOptionalType(x: unknown): x is OptionalType<any>;
```

Defined in: [packages/common/src/Type.ts:4374](https://github.com/evoluhq/evolu/blob/e7144e2bbe9069362b62dec1b64a8aa922b8f1b0/packages/common/src/Type.ts#L4374)

Determines if a given type is an [OptionalType](https://evolu.dev/docs/api-reference/common/Type/interfaces/OptionalType).