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!

Inizia con la riproduzione collegata in TypeScript Playground e confronta il JavaScript emesso con l’ordine di inizializzazione segnalato. Traccia il modo in cui il verificatore dei tipi gestisce l’inizializzazione delle proprietà statiche durante la costruzione, quindi determina se il completamento debba essere una diagnostica, una modifica all’emissione o una decisione di progettazione esplicita; verifica il risultato con un caso di regressione.