TS2333: 'this' cannot be referenced in constructor arguments

Suggestion

✅ Viability Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, new syntax sugar for JS, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

⭐ Suggestion

TypeScript disallows this:

class A {
    constructor(readonly b: B = new B(this)) {}
}
class B {
    constructor(a: A) {}
}

TS2333: 'this' cannot be referenced in constructor arguments

Instead, we can rewrite it as follows.

class A {
    readonly b: B;
    constructor(b?: B) {
        this.b = b ?? new B(this);
    }
}
class B {
    constructor(a: A) {}
}

However, this is clearly more verbose. Since this transformation is always possible, it seems TypeScript should allow this in the constructor and be doing the job of rewriting it for us, so we can maintain simpler code using the former constructor argument approach.

📃 Motivating Example

Permitting this references in constructor arguments simplifies object initialization.

💻 Use Cases

Creating classes at construction time that reference the creating class.

Inizia tracciando la diagnosi TS2333 e i controlli del compilatore per this negli argomenti del costruttore; l'issue non indica file o test specifici. Confronta gli esempi di costruttori proposti con il JavaScript emesso e con il comportamento esistente del controllo dei tipi, e considera test che stabiliscano quando il riferimento dovrebbe essere accettato senza modificare l'output a runtime.