Destructuring assignment with computed property name does not help narrow types as intended.

[hkleungai]

🔎 Search Terms

"destructuring assignment", "computed property name", "type narrowing"

🕗 Version & Regression Information

Happen to all existing version in typescript playground.

⏯ Playground Link

https://tsplay.dev/w1eElw

💻 Code

declare let obj: Record<string, string>

declare let cond: boolean;
declare let key: string;
let result: string | null = null;

if (cond) {
    ({ [key]: result } = obj);
    result;
//  ^?
}

if (cond) {
    ({ 'key': result } = obj);
    result;
//  ^?
}

🙁 Actual behavior

Type narrowing did not happen to the assignee variable result after the assignment ({ [key]: result } = obj);.

🙂 Expected behavior

Expecting the assignment ({ [key]: result } = obj); will narrow the assignee variable result to non-null.

Additional information about the issue

No response

[hkleungai]

Looks like this one is just another duplicate of #61957.

Feel free to close this issue. Feel like the fix is not gonna happen in short term.

[Andarist]

@RyanCavanaugh I think @hkleungai might came to the wrong conclusion here.

The other issue is about CFA for an element access expression with variable access - this one here is about imprecise CFA for a variable that just happens to be related to a variable binding element. After all, those are really the same and it looks to me that they could very well just work the same: TS playground

[typescript-bot]

This issue has been marked as "Duplicate" and has seen no recent activity. It has been automatically closed for house-keeping purposes.

[hkleungai]

Hi @Andarist @RyanCavanaugh, does the typescript team still want to treat this issue as a duplicate of #61176 or #61957? Or is it a "new" issue to be resolved?