@SharkChips openMenu and related methods return promises since beta.7. If for some reason the splitter cannot open or close (because it’s already open/closed, another splitter is open, etc.), it will reject the promise and this is printed on the console if you don’t handle it with catch. I think we will modify this behavior because it could be a bit annoying. In any case, you don’t need to worry about those error messages now since they don’t affect your app.