CODEWITHSUNDEEP
typescript
Reynicke
Reynicke

Reputation: 1550

TypeScript "Not a constructor function type" error after casting

I have the following TypeScript code:

class ClassA {
  field1: any;
}

const SomeClassAsA = diContainer.get('SomeClass') as ClassA;

class ClassB extends ClassA {} // works
class ClassB extends SomeClassAsA {} // error: Type ClassA is not a constructor function type

Why can ClassB be extended with ClassA but not with some other Object casted as ClassA? In need to extend SomeClass. How can I accomplish that?

I use TypeScript 1.5.3

Upvotes: 0

Views: 1518

Answers (1)

Alex Wayne
Alex Wayne

Reputation: 187034

const SomeClassAsA = diContainer.get('SomeClass') as typeof ClassA;
//                                                   ^ added

When you use a class as a type, you are actually typing an instance of that class. Remember, that a class is a real object in javascript, not like an interface which has no raw javascript corollary.

This makes sense, because it allows you to write:

const person: Person = new Person()

person is clearly and an instance of Person and not the class constructor object Person.

So to get the the type of the class itself, use the typeof operator.

Working playground

Upvotes: 1

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