The goal is to declare a Record type definition for a mapper in order to restrict the keys and function values.
The arguments of those functions have different behaviors, thus are defined using a union type.
PushNotificationPayloadVideoComment is part of PushNotificationPayload union type, but the TS compiler detects that it’s not assignable to its union
TypeScript version: 4.3.2
Click here for the full code snippet on TS Playground
>Solution :
Using unknown means the function assigned should be capable to handle any parameter type, and you are using functions that can only handle a specific type.
You could use a custom mapped type to map each callback to the appropriate parameter type:
type Mapper = {
[P in PushNotificationPayload as P['category']]?: (payload: P) => void
}