Definite assignment assertion in JS not flagged

[Josh-Cena]

Bug Report

Noted by someone on Discord.

🔎 Search Terms

non null assertion javascript error

Related #17222

🕗 Version & Regression Information

• This is the behavior in every version I tried

⏯ Playground Link

Playground link with relevant code

💻 Code

const a = { a!: 1 };

🙁 Actual behavior

There's no error; crashes at runtime

🙂 Expected behavior

There should be an error

[DanielRosenwasser]

Uh, forget JavaScript - does it ever make sense to have a definite assignment assertion on an object property declaration?

let obj = {
    wat!: 123
}

The only instance I can actually think of is on a shorthand property which would act more as a non-null assertion than a definite assignment assertion... but ironically, we issue an error if you try to do that!

declare function tryGetNumber(): number | undefined;

let num = tryGetNumber();
let obj = {
    num!
//     ~
// A definite assignment assertion '!' is not permitted in this context.
};

[Josh-Cena]

So my original post is already an error since TS 4.8. However, there's still not specialized check in JS files for the following:

class A {
  a!;
}

Could this issue be about making the above an error?