Properties of instances of anonymous classes have type <any> after an instanceof guard.

TypeScript Version: 2.4.1

Code

function create_my_class<T>() {
    return class {
        value: T;
        constructor(
            value: T
        ) {
            this.value = value;
        }
    }
}
const MyClassWithNumber = create_my_class<number>();
const with_number = new MyClassWithNumber(234);

with_number.value = 10;
// with_number.value = "sdf"; // error, and rightly so

const something: any = with_number;

if(something instanceof MyClassWithNumber) {
    something.value = 20;
    something.value = "sdf"; // not an error, but should be one
}

Expected behavior:
The last assignment should be marked as a type error by TS.

Actual behavior:
The last assignment is not marked as error. This is somewhat surprising, as the line

with_number.value = "sdf";

is righteously reported as a type error by TS.

Not a huge issue, but prevented me from using a class factory.

Inizia con la riproduzione TypeScript fornita e segui come il controllo instanceof restringe il valore restituito dalla factory generica di classi. Verifica il comportamento usando le assegnazioni mostrate, quindi assicurati che l’assegnazione protetta di tipo stringa venga segnalata come errore di tipo, mentre l’assegnazione numerica rimanga valida.