Function onStart

onStart(cb: LifecycleMethod, opts?: LifecycleMethodOptions): () => void
Register a callback in the engine start event.
This happens at the beginning of each frame
Parameters
- cb: LifecycleMethod
  The callback to be called
- Optionalopts: LifecycleMethodOptions
Returns () => void
A function that can be called to unregister the callback
Example
```
onStart((ctx : Context) => {
    // do something
}
```