Why TDZ checks are not implemented (original) (raw)

Bug Report

It may not be a bug, because I see that you clearly know what TDZ check is (such as the code example in this issue), but it is not applied. I did find some related issues reported by TypeScript team members such as #5174 several years before, but it still passes the check now.

Just out of curiosity, would you please explain why such checks are not (fully) implemented?

🔎 Search Terms

TDZ check

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries.

⏯ Playground Link

Playground link with relevant code

💻 Code

// https://github.com/microsoft/TypeScript/issues/5174 function f(x: number) { switch(x) { case 1: let x = 1; case 2: x = 2; // should be error because of TDZ } }

// https://github.com/microsoft/TypeScript/issues/52924#issue-1595962667 function h() { let result = g(); let x: number = 10; return result;

function g() {
    return x;
}

}

🙁 Actual behavior

No error reported.

🙂 Expected behavior

TDZ check should be applied.