How to get useManagerState?
import useManagerState from 'fontoxml-fx/src/useManagerState.js'
A React hook which allows you to register a notifier and a getManagerState function. When this hook is initialized a notifier callback is registered. Whenever this callback is invoked, getManagerState will be called and put into React state (using a useState hook).
Note that it's required to provide a bound function to getManagerState if you want to access the instance properties (using "this"). You can do this by either making the provided function an arrow function or using Function.prototype.bind() in the class constructor.