Static variable may be undefined when constructing an object of the same class

Bug Report

I'm not sure whether this may be a issue that can be fixed or just keep it as is "by design". I haven't found any other issues similar to this one here, at least with the search terms I tried (sorry if someone else already reported this 🙂).

🔎 Search Terms

static, undefined, uninitialized, constructor

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about static variables, variable order initialization, etc., but none of them seem to match this.

At the moment of writing this, TypeScript version is 4.2.3.

⏯ Playground Link

Playground Link

💻 Code

class A {
    public static readonly instance: A = new A();
    public static readonly constant: number = 1;
    
    public constructor() {
        console.log(A.constant, A.constant * 5);
        console.log(A.constant.toString());
    }
}

🙁 Actual behavior

When calling the constructor to initialize the static variable instance, A.constant is not yet initialized (it's undefined), so the constructor logs undefined, NaN.

In addition, A.constant.toString() gives a javascript execution error, which even in strict mode the compiler doesn't catch.

🙂 Expected behavior

The compiler could tell that constant has type number | undefined at that moment (manually changing the type of constantto number | undefined correctly yields a compiler error) or even rearrange the generated javascript to initialize first constant and then instance (which I think it may be more difficult in more complex scenarios).

Thank you very much!

リンクされた TypeScript Playground の再現から始め、出力された JavaScript と報告された初期化順序を比較します。構築時に型チェッカーが静的プロパティの初期化をどのように処理するかを追跡し、そのうえで、補完を診断にするのか、出力を変更するのか、明示的な設計判断とするのかを判断します。回帰ケースで結果を検証します。