infer err in catch(err) {} as unknown

[gerardolima]

Suggestion

I think the inferred type for err in catch (err) { } should be unknown, which it is, instead of any which is unsafe and highly discouraged. unknown is safer and provides better semantics; I really don't understand why this is not the default for tsc.

🔍 Search Terms

catch exception type inference infer unknown any

✅ Viability Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, new syntax sugar for JS, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

⭐ Suggestion

Infer the type for err in catch (err) { } as unknown

📃 Motivating Example

This is valid Typescript 4.2.3 code as shown here

try { throw new Error() } catch(err) { console.log(err.potato) }

💻 Use Cases

What do you want to use this for?

Improve type safety to catch blocks.

What shortcomings exist with current approaches?

catch(err) {} infer the type of err as any

What workarounds are you using in the meantime?

catch (err: unknown) {}

[whzx5byb]

See #41016

[gerardolima]

hey, @whzx5byb, #41016 advocates for a compiler flag to enable this behaviour. I advocate this to be the default behaviour. Other than that, it's the same. Should I close this issue, then?

[whzx5byb]

I think this should not be the default behavior since it would bring breaking changes.

[MartinJohns]

@gerardolima Why do you believe changing the default type to a more restrictive one won't be a breaking change?

[x] This wouldn't be a breaking change in existing TypeScript/JavaScript code

[gerardolima]

hey, @MartinJohns, I think this would enforce correct type checks on optimistic code. Nevertheless, this issue was flagged as duplicate (I think related to #41016).

[Stirfry70]

Not sure what you mean?Sent using the mobile mail appOn 06/05/2021 at 2:10 PM, Gerardo Lima wrote: From: "Gerardo Lima" ***@***.***>Date: 6 May 2021To: "microsoft/TypeScript" ***@***.***>Cc: "Subscribed" ***@***.***>Subject: Re: [microsoft/TypeScript] infer `err` in `catch(err) {}` as `unknown` (#43960) hey, @MartinJohns, I think this would enforce correct type checks on optimistic code. Nevertheless, this issue was flagged as duplicate (I think related to #41016). —You are receiving this because you are subscribed to this thread.Reply to this email directly, view it on GitHub, or unsubscribe. [ { ***@***.***": "http://schema.org", ***@***.***": "EmailMessage", "potentialAction": { ***@***.***": "ViewAction", "target": "#43960 (comment)", "url": "#43960 (comment)", "name": "View Issue" }, "description": "View this Issue on GitHub", "publisher": { ***@***.***": "Organization", "name": "GitHub", "url": "https://github.com" } } ]

[typescript-bot]

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