Extending string-based enums

Before string based enums, many would fall back to objects. Using objects also allows extending of types. For example:

const BasicEvents = {
    Start: "Start",
    Finish: "Finish"
};

const AdvEvents = {
    ...BasicEvents,
    Pause: "Pause",
    Resume: "Resume"
};

When switching over to string enums, it"s impossible to achieve this without re-defining the enum.

I would be very useful to be able to do something like this:

enum BasicEvents {
    Start = "Start",
    Finish = "Finish"
};

// extend enum using "extends" keyword
enum AdvEvents extends BasicEvents {
    Pause = "Pause",
    Resume = "Resume"
};

Considering that the produced enums are objects, this won"t be too horrible either:

// extend enum using spread
enum AdvEvents {
    ...BasicEvents,
    Pause = "Pause",
    Resume = "Resume"
};

まず issue の string-enum と object-spread の例を確認し、続いて enum 構文と出力される JavaScript が現在どのように定義されているかを調べます。型チェックと生成されるオブジェクトの動作を含め、意図されている継承または spread のセマンティクスを明確にし、その提案が既存の enum と互換性があることを検証します。