```typescript
import { types } from "node:node__util.d.ts";
```
isWeakMap(object: unknown): object is WeakMap<object, unknown>
Returns `true` if the value is a built-in [`WeakMap`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap) instance.
```js
util.types.isWeakMap(new WeakMap()); // Returns true
```