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

```ts
const assertInstanceOf: <Constructor>(
  value: unknown,
  constructor: Constructor,
) => asserts value is InstanceType<Constructor>;
```

Defined in: [packages/common/src/Assert.ts:688](https://github.com/evoluhq/evolu/blob/ecbac001e0c18bbc45b44715f49ecc3a768c5ec9/packages/common/src/Assert.ts#L688)

Asserts that a value is an instance of a constructor and narrows it.

### Example

```ts

const value: unknown = new TypeError("Invalid value.");
assertInstanceOf(value, TypeError);
assertType<typeof value, TypeError>();
```