Allow an interface in the JSX namespace to specify the element class type

We're writing a non-react library that uses TS's JSX support with custom interfaces defined in the JSX namespace. Unless we are very much mistaken (The documentation seems a little out-of-date in this area? Most of our current understanding comes from reading through issues on here, we may have missed something.) it seems that while ElementClass can be used to define the type of the element instance type there is no interface to limit the members of the element class type.

We have a custom component base-class and an equivalent to React's createElement function. Our createElement function needs to be able to create instances of the component classes. To be able to do this in a type-safe manner, we need to be able to specify an interface for the element class type that can require a specific constructor signature.

This feels like an oversight in the current implementation TBH. With React itself it's even possible to create components with incompatible constructors that would fail at runtime.

Inizia esaminando il supporto di TypeScript per il namespace JSX, in particolare ElementClass e lo scenario createElement personalizzato descritto nell’issue. Determina come un’interfaccia per il tipo della classe dell’elemento dovrebbe esprimere un requisito per il costruttore. Il lavoro è completato quando il controllo dei tipi JSX può applicare tale requisito ai componenti personalizzati senza compromettere il comportamento JSX esistente.