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

🔎 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

Commencez par la reproduction liée dans TypeScript Playground et comparez le type inféré de result après l’affectation par déstructuration d’une propriété calculée et l’affectation d’une propriété littérale. Suivez le comportement de narrowing de type impliqué et vérifiez que la modification terminée conserve le narrowing non-null attendu dans les deux exemples.