onChangeStart event doesn't return value

There are 3 events
```
onChange?(value: number): void;
onChangeComplete?(value: number): void;
onChangeStart?(value: number): void;
```

only `onChange` returns value the other ones return class instance

<img width="1060" alt="Screen Shot 2021-01-29 at 12 52 14 AM" src="https://user-images.githubusercontent.com/13457544/106197853-9a9af000-61cc-11eb-96b4-dc9a8bac4f6d.png">
