onError for useSubscription

[ArnaudBarre]

Problem:

Do a side effect on subscription error using the useSubscription hook.

Current solution:

const { error } = useSubscription<UserInteraction>(
  SUBSCRIBE_USER_INTERACTIONS,
  {
    onSubscriptionData: ({ subscriptionData }) => {
      if (subscriptionData.error) // bad typing, never set
      if (!subscriptionData.data) return; // bad typing, not called if no data
      ... // side effect on data
    },
  }
);

useEffect(() => {
  if (!error) return;
  ... // side effect on error
}, [error]);

Desired API:

useSubscription<UserInteraction>(
  SUBSCRIBE_USER_INTERACTIONS,
  {
    onSubscriptionData: ({ subscriptionData }) => {
      ... // side effect on data (with subscriptionData.data! and no subscriptionData.error)
    },
    onError: (error: ApolloError!) => {
      ... // side effect on error
    },
  }
);

Why:

I think this will make the API more consistent with useQuery and avoid null checks in callbacks, making the code more readable.

[eddie-atkinson]

Did anyone find any other ways of achieving this? Has there been any progress on this request?