Discover one among numerous interfaces available for handling Promise responses

My API handler returns a promise of a type. The object returned can be one of the following interfaces, depending on the API response:

export interface Event {
  statusCode: number
}

export interface CreateEvent extends Event {
  data: Object
}

export interface Forbidden {
  message: string
}

However, I am facing issues with the types during testing. The error message

this value doesn't exist on type:
indicates a missing value from Forbidden when it was supposed to be a successful response.

My expected types are:

type ApiResponse = Forbidden | Event | CreateEvent

or

export enum ApiResponse {CreateEvent, Forbidden, Event}

When I set the API function return type to:

callApi = (event: Event): Promise<ApiResponse>   => {...}

I'm unsure about what ts expects in this situation. It seems like a basic behavior, but I can't figure it out.

Answer №1

When a function has the potential to return one of three values, employing a Type Guard or Type Assertion function becomes crucial in determining the specific outcome.

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