Repository navigation
Optional discriminated union's callback parameter type is not inferred #35769
Description
discriminated union
Code
type T1 = {
as?: 'button',
onClick?: (el: number) => void
}
type T2 = {
as: 'a',
onClick?: (el: string) => void
}
type T = T1 | T2;
// onClick first parameter type is inferred according to T1 (number)
const myT1_1: T = {
as: undefined,
onClick: _ev => {}
}
// onClick first parameter type is inferred according to T1 (number)
const myT1_2: T = {
as: 'button',
onClick: _ev => {}
}
// onClick first parameter type is inferred according to T2 (string)
const myT2_1: T = {
as: 'a',
onClick: _ev => {}
}
// onClick first parameter type is not inferred (any)
const myT1_3: T = {
onClick: _ev => {}
} Expected behavior:
onClick _ev parameter of myT1_3 is inferred to be a number
Actual behavior:
onClick _ev parameter of myT1_3 is any
Playground Link:
Playground Link
If the callback in T1 and T2 is replaced with a primitive member then myT1_3 is inferred correctly. Playground Link
Activity
wvanvugt-speedline commentedon Feb 5, 2021
This appears to be a duplicate of #41759
IanVS commentedon Jun 4, 2021
The parameter seems to be correctly inferred in the latest version of typescript, can this be closed as fixed?
RyanCavanaugh commentedon Jun 11, 2021
Confirmed fixed 4.2 -> 4.3
wzono commentedon Nov 18, 2021
Ryan Cavanaugh (@RyanCavanaugh) Still exist in the last version..
https://www.typescriptlang.org/play?ts=4.5.0-beta#code/C4TwDgpgBAglC8UDeAoK6qkgfgFxQHIYCAaNDAQ3wAoBjfJKAE3wDsBXAWwCMIAnKAF8AlAgB8UAG4B7AJZMA3CkEoUWaACEEycunX4CG0rqhUodBszZdefElHpQAzsD6zWAcyGj4EmfKUVVXVYDQBhbTgAHygtJRRJCgEzGHCAbQBdKBiAJQhaaT4mAB4XN097VLDMiUQ0k1QMJtMaMCSKTicfCUbmvpMmlUGUDKA