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1. andrewbranch commented on Aug 31, 2021

   

   Andrew Branch (andrewbranch)

   on Aug 31, 2021

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   The type for .catch(...) callback parameters is defined in lib files, so we’d have to expose a new type that acts like unknown or any depending on compilation settings... and I’m not sure we’d want that type escaping into the wild 😬. This is a compelling use case, though.
2. Andrew Branch (andrewbranch)

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   on Aug 31, 2021
3. Cellule commented on Oct 5, 2021

   

   Michael "Mike" Ferris (Cellule)

   on Oct 5, 2021

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   You can easily achieve this by overloading the signature of Promise.catch in your project

   // Promise.d.ts
   interface Promise<T> {
     /**
      * Attaches a callback for only the rejection of the Promise.
      * @param onrejected The callback to execute when the Promise is rejected.
      * @returns A Promise for the completion of the callback.
      */
     catch<TResult = never>(
       onrejected?: ((reason: unknown) => TResult | PromiseLike<TResult>) | undefined | null,
     ): Promise<T | TResult>;
   }

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4. yoav-lavi commented on Oct 5, 2021

   

   Yoav Lavi (yoav-lavi)

   on Oct 5, 2021

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   Michael "Mike" Ferris (@Cellule) Thanks for the snippet, yes, you can do this yourself, but the goal of this suggestion is to add this to TS itself

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5. fregante commented on Dec 6, 2021

   

   fregante

   on Dec 6, 2021

   Last edited by fregante

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   Michael "Mike" Ferris (@Cellule) thanks for that! Unfortunately it doesn't cover allSettled though and I wasn't able to override that:

   interface PromiseRejectedResult {
     status: "rejected";
     // @ts-expect-error TS2717 even if overridden, it doesn't work
     reason: unknown;
   }

   https://www.typescriptlang.org/play?target=7#code/IYZwngdgxgBAZgV2gFwJYHsIwG4FMBOYehEqUuAFAJQwDeAUDEzFJiMjAA77oC2qIXCBgBeGMADuwVBwAKPfoIB0wADaqAyrmTJVuACYUA2gEYAulUbM46fDAqsI7LgoG4Y6OC75uQNBszMqF4U3D7K7MDICMIicTAARPi4AFa4UMgGCf5WgUxhirhKyaCYucwAvuVVFUA

   
6. emartinfigma commented on Feb 11, 2022

   

   Evan Martin (emartinfigma)

   on Feb 11, 2022

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   You can easily achieve this by overloading the signature of Promise.catch in your project

   I tried this, but it seems like TS just selects the 'any' overload if the signatures don't match. Playground
7. thw0rted commented on Apr 6, 2022

   

   James Bromwell (thw0rted)

   on Apr 6, 2022

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   I'd really like to see this implemented, and I think it's a shame it wasn't considered for release alongside useUnknownInCatchVariables. Before the flag existed, you could always freely convert between

   • p.then(good, bad)
   • p.then(good).catch(bad), and
   • try { result = await p; good(result) } catch (err) { bad(err); } (in async context)

   Now, if bad doesn't expect unknown it will fail, but only in the last of these forms. I want a flag that says "use unknown type for all errors", including try/catch and Promise rejection -- which are the same thing, under async/await!
8. ExE-Boss commented on Apr 10, 2022

   

   ExE Boss (ExE-Boss)

   on Apr 10, 2022

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   James Bromwell (@thw0rted)

   • p.then(good, bad)
   • p.then(good).catch(bad)

   Are not the same, since if good throws an error, only the latter form will catch it.

   ---

   p => p.then(good, bad) is actually equivalent to:

   async p => {
   	let result;
   	try {
   		result = await p;
   	} catch (err) {
   		return bad(err);
   	}
   
   	return good(result);
   }
9. thw0rted commented on Apr 10, 2022

   

   James Bromwell (thw0rted)

   on Apr 10, 2022

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   That's correct, but I didn't mean that those forms were identical, I was only referring to the parameter type of the bad function. The point is that the then-callback gets any while the catch-block invocation gets unknown.

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10. NotWoods commented on Jul 26, 2024

    

    Tiger Oakes (NotWoods)

    on Jul 26, 2024

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    Could the approach used to fix iterator types in #58243 be used to fix promise.catch as well?

    Similiar to the BuiltinIteratorReturn type, perhaps a PromiseCatchErrorType can be used that would be either any or unknown depending on a compiler flag.

    interface Promise<T> {
        catch<TResult = never>(onrejected?: ((reason: PromiseCatchErrorType) => TResult | PromiseLike<TResult>) | undefined | null): Promise<T | TResult>;
    }
11. jfxio commented on Jan 6, 2025

    

    Joe F (jfxio)

    on Jan 6, 2025

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    Probably obvious, but slight extension to Michael "Mike" Ferris (@Cellule)'s Promise type to also infer unknown for the onrejected then() parameter. This covers both bad uses in James Bromwell (@thw0rted)'s reply.

    // Promise.d.ts
    interface Promise<T> {
      then<TFul, TRej = never>(
        onfulfilled?: ((value: T) => TFul | PromiseLike<TFul>) | null,
        onrejected?: ((reason: unknown) => TRej | PromiseLike<TRej>) | null,
      ): Promise<TFul | TRej>
    
      catch<TRej = never>(
        onrejected?: ((reason: unknown) => TRej | PromiseLike<TRej>) | null,
      ): Promise<T | TRej>
    }

    Node 20.12, TS ^5.7.2 w/ target & lib = ESNext

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