Questions interpreting the spec for my book

[jisaacks]

I am in the process of writing a book for Manning Publications on the newest JavaScript features, including future features that are in popular use (such as decorators)

I have some questions from the current stage-2 proposal that I would greatly appreciate if I could get answered so that I may provide the latest accurate information in my book.

It seems like class decorator function takes 3 arguments, the class/constructor being decorated, the parent class/constructor, an array of member descriptors.

• If the class does not explicitly extend another class (no super), will the heritage be set as Object, null, undefined or something else?

The member decorator functions accept and return member descriptors.

• The value for kind may be "Property", I am assuming "Method" and "Accessor" are other possibilities. Does case matter? Any others?
• I am assuming key refers to the name of the member, and thus can be changed like so:

function rename(md) {
  return Object.assign({}, md, {key: 'bar'})
}

class A {
  @rename foo = 1;
}

new A().bar // 1

• It looks like extras is an optional array of member descriptors. What is the purpose of this?
• It looks like finished is an optional function, what is the purpose of this?

Thanks so much.

[jkrems]

Disclaimer: Not one of the maintainers/authors. But I think I can answer some of the questions.

• extras allows to explode one property into multiple properties. Example: Generate default getX and setX accessor methods for a private property.

• finished allows to operate on the 100% definitely final class reference. E.g. if I'd want to store meta data about the class, keyed by the class (myWeakMap.set(TheClass, metaData)), I would run into problems if there's a class decorator that might wrap the original class. By running such code in the finisher, I can be certain that future attempts of looking up the meta data will succeed.

[littledan]

This proposal is still in development; I'd be hesitant to publish a hard-copy book about its details. The answers have actually changed since the time you wrote these questions. I'll get back to you with current answers soon.