"Decorators are not valid here" for methods inside an instantiated class

[nevir]

TypeScript Version: 1.8.10

Code

export default new class Foo {
  @someDecorator
  someMethod() {}
}

Will result in an error on @someDecorator:

error TS1206: Decorators are not valid here.

---

It can be worked around via

class Foo {
  @someDecorator
  someMethod() {}
}
export default new Foo();

[mhegazy]

duplicate of #7342