Allowing extracting ReturnType of wrapped function with generics

[dogukanakkaya]

Suggestion

Allowing extracting ReturnType of wrapped function with generics.

export function query() {
  const getData = <T extends string>(select: T = 'id,name' as T) => {
    return db.from('table').select(select)
  }
  
  return { getData }
}

type QueryWrapper = ReturnType<typeof query>

type DataWithIdAndName = ReturnType<QueryWrapper['getData']<'id,name'>>
// type DataWithIdAndName = Awaited<ReturnType<QueryWrapper['getData']<'id,name'>>>
// type DataWithIdAndName = NonNullable<Awaited<ReturnType<QueryWrapper['getData']<'id,name'>>>>

🔍 Search Terms

• Typescript ReturnType with args
• Typescript wrapped function ReturnType with args
• Typescript ReturnType with generic definition

✅ 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.

💻 Use Cases

export function query() {
  const getData = <T extends string>(select: T = 'id,name' as T) => {
    return db.from('table').select(select)
  }
  
   return { getData }
}

const data = await query().getData('id,name') // this is already infered since the underlying library already returns correct types depending on select value (in my case supabase)

But when it's needed to extract that return type and use it in somewhere else. For example in a React Component that is passed as prop. I need to extract the type of getData with the generic select value that is provided.

Possible workarounds at the moment

Set generic into wrapper

export function query<T extends string>() {
  const getData = (select: T = 'id,name' as T) => {
    return db.from('table').select(select)
  }
  
   return { getData }
}
// this results with other type errors.

Or write another function and get it's type. Which is just duplication.

const fn = await query().getData('id,name')
type FnReturn = Awaited<ReturnType<typeof fn>>

[fatcerberus]

Your query function as written doesn’t actually return anything, but I’m going to assume that was a transcription error.

This looks like a duplicate of #40179.

[dogukanakkaya]

Just updated the return.

It looks like a duplicate but not exactly. Wrapped functions are bit more different. If it wasn't wrapped, i could just pass generic to that function easily with. ReturnType<typeof getData<'id,name'>>

[typescript-bot]

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