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

```ts
type IsUnion<T, Whole> = [T] extends [never]
  ? false
  : T extends Whole
    ? [Whole] extends [T]
      ? false
      : true
    : never;
```

Defined in: [packages/common/src/Types.ts:458](https://github.com/evoluhq/evolu/blob/037c390af081e9944d616ff298a729515c5c5ab7/packages/common/src/Types.ts#L458)

Returns whether a type is a union.