.throwOnError() only adjusts types correctly if await is used and is still incorrect if you use `then`

[MrPiao]

Bug report

• I confirm this is a bug with Supabase, not with my own application.
• I confirm I have searched the Docs, GitHub Discussions, and Discord.

Describe the bug

awaiting a query with .throwOnError() correctly eliminates null from the typing. However, if you don't await it and use .then(...) instead, then null is not eliminated from the typing.

To Reproduce

supabase.from('users').select('id').eq('id', id).single().throwOnError().then(({ data }) => { ... });

Expected behavior

Type of data should be { id: string }

Actual behavior

Type of data is { id: string } | null

[MrPiao]

My guess is that supabase/postgrest-js#563 did not cover this use case and it was not automatically fixed because it uses non-standard Promise objects

[andrewtsarow]

A temporary workaround that worked well for me is adding a small utility to assert the data type after .throwOnError():

export function assertData<T>(response: { data: T | null }): { data: T } {
  return { ...response, data: response.data! }
}

Then you can safely chain it like this:

const { data } = await supabase
  .from('your_table')
  .select('*')
  .throwOnError()
  .then(assertData)

This ensures that data is properly typed without null after .throwOnError(). Hopefully this helps others until the typing issue is resolved!