[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) › assertNotUndefined

```ts
const assertNotUndefined: <T>(
  value: T,
  message?: string,
) => asserts value is T & ({} | null);
```

Defined in: [packages/common/src/Assert.ts:804](https://github.com/evoluhq/evolu/blob/ecbac001e0c18bbc45b44715f49ecc3a768c5ec9/packages/common/src/Assert.ts#L804)

Asserts that a value is not undefined while preserving null.

### Example

```ts
import {
  assertEqual,
  assertErr,
  assertInstanceOf,
  assertNotUndefined,
  assertType,
  trySync,
} from "@evolu/common";

const value = null as string | null | undefined;
assertNotUndefined(value);
assertType<typeof value, string | null>();
assertEqual(value, null);
const result = trySync(() => assertNotUndefined(undefined));
assertErr(result);
assertInstanceOf(result.error, Error);
assertEqual(result.error.message, "Expected value not to be undefined.");
```