Why can't typescript discriminate based on a common property like this? After reading the docs I thought this would work.
Heres a typescript playground
type Mammal = { legs: number }
type Fish = { fins: number }
type Action1 = {
type: 'a',
payload: Mammal
}
type Action2 = {
type: 'b',
payload: Fish
}
type ActionUnion = Action1 | Action2
const A: Action1 = { type: 'a', payload: { legs: 4 } }
const B: Action2 = { type: 'b', payload: { fins: 3 } }
function foo(action: ActionUnion) {
switch (action.type) {
case 'a':
const { legs } = action.payload
case 'b':
const { fins } = action.payload
default:
break
}
}
You forgot to break your case statement. Should look like this
case 'a':
const { legs } = action.payload
break;
case 'b':
const { fins } = action.payload
They do work like that, but your switch case was falling through to the next case, add a break
and it will work
type Mammal = { legs: number }
type Fish = { fins: number }
type Action1 = {
type: 'a',
payload: Mammal
}
type Action2 = {
type: 'b',
payload: Fish
}
type ActionUnion = Action1 | Action2
const A: Action1 = { type: 'a', payload: { legs: 4 } }
const B: Action2 = { type: 'b', payload: { fins: 3 } }
function foo(action: ActionUnion) {
switch (action.type) {
case 'a':
const { legs } = action.payload
break;
case 'b':
const { fins } = action.payload
break;
default:
break
}
}
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