8000 `unknown` should narrow to `{}` when non-null · Issue #48928 · microsoft/TypeScript · GitHub
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unknow 8000 n should narrow to {} when non-null #48928

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paulferaud opened this issue May 3, 2022 · 2 comments
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unknown should narrow to {} when non-null #48928

paulferaud opened this issue May 3, 2022 · 2 comments
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@paulferaud
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Bug Report

🔎 Search Terms

empty type, unknown, top type, unknown not null

🕗 Version & Regression Information

Starting 3.0 (when unknown was introduced) and until at least 4.6.2

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

⏯ Playground Link

Playground link with relevant code

💻 Code

let myUnknown: unknown = null
let myEmpty: {} = myUnknown ?? 5
if (myUnknown != null) {
    let myEmpty2: {} = myUnknown
}

🙁 Actual behavior

Type 'unknown' is not assignable to type '{}'. (2322)

🙂 Expected behavior

I believe narrowing should be happening. unkown is the top type for everything. {} is the top type for everything non-null non-undefined. Therefore, when an unknown is or'ed (|| or ??) with a non-null, or if checked not-null itself (if (myUnknown != null)), then the result should be narrowed to {}.

Extra context: I'm trying to wrap around JSON.parse to return {} when the result is null. I would have expected that:

JSON.parse(arg) ?? {}

Be of the type {}, but TypeScript is insisting that it's actually unknown.
@MartinJohns
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Duplicate of #32347. Used search terms: narrow unknown in:title

@andrewbranch andrewbranch added the Duplicate An existing issue was already created label May 3, 2022
@typescript-bot
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This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.

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@andrewbranch @MartinJohns @typescript-bot @paulferaud
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