Utility type ConstructorParameters

Constructs a tuple or array type from the types
of a constructor function type. It produces a
tuple type with all the parameter types (or the
type never if Type is not a function).

class C {
  constructor(a: number, b: string) {}
}

type T3 = ConstructorParameters<typeof C>;  
type T3 = [a: number, b: string]