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!

Start with the linked TypeScript Playground reproduction and compare the emitted JavaScript with the reported initialization order. Trace how the type checker handles static property initialization during construction, then determine whether completion should be a diagnostic, an emission change, or an explicit design decision; verify the result with a regression case.