# ObservableMixinConstructor

typedef

Constructor returned by [`ObservableMixin`](module_utils_observablemixin.md#function-ObservableMixin:EXTENDS). Use it to name a mixin base class before extending it.

```typescript
const MyObservableBase: ObservableMixinConstructor<typeof BaseClass> = ObservableMixin( BaseClass );

class MyObservable extends MyObservableBase {}
```

[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-utils/src/observablemixin.ts#L39)

<a id="type-parameters">

## Type parameters

### `Base: extends Constructor<Emitter>`

#### Value

`Mixed<Base, Observable>`

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Full index of the CKEditor 5 API reference: [llms.txt](llms.txt)