data and error cannot be undefined by themselves

[0x009922]

Problem

interface SomeDataType {
  foo: string;
}

async function fetcher(): Promise<SomeDataType> {
  return { foo: 'test' }
}

const { data, error } = useSWRV('some-key', fetcher);

// const data: Ref<SomeDataType | undefined> | undefined
// const error: Ref<any> | undefined

Why can the values data and error themselves be undefined? This is not really what is happening. They are always some kind of Ref with values, they cannot be undefined by themselves. The code snippets below confirm this.

// https://github.com/Kong/swrv/blob/03b853191cb00d48f51f8edbdbbe3216e8847bf5/src/use-swrv.ts#L203

stateRef = reactive({
  data: undefined,
  error: undefined,
  isValidating: true,
  key: null
}) as StateRef<Data, Error>

// -- snip --

// https://github.com/Kong/swrv/blob/03b853191cb00d48f51f8edbdbbe3216e8847bf5/src/use-swrv.ts#L389

const res: IResponse = {
  ...toRefs(stateRef),
  mutate: (data, opts: revalidateOptions) => revalidate(data, {
    ...opts,
    forceRevalidate: true
  })
}

return res

This code shows that data and error will always be Ref<Data> and Ref<Error>, not Ref<Data> | undefined and Ref<Error> | undefined.

I think the IResponse interface should be fixed:

// now
export interface IResponse<Data = any, Error = any> {
  data?: Ref<Data | undefined>;
  error?: Ref<Error | undefined>;
  isValidating: Ref<boolean>;
  mutate: () => Promise<void>;
}

// should be
export interface IResponse<Data = any, Error = any> {
  data: Ref<Data | undefined>;
  // ^ remove '?'
  error: Ref<Error | undefined>;
  // ^ remove '?'
  isValidating: Ref<boolean>;
  mutate: () => Promise<void>;
}

Anyway, thanks for the swrv, it's great!

[darrenjennings]

This is a duplicate of #74. @lqdsld can you provide a reproduction repo that shows the type error?