fromEvent in v7

[pratikgaikwadhive]

We use rethinkdb in our project. In v6 of rxjs I could write

const event$ = rxjs.merge<Changes<IGuest>, RethinkDBError>(
      rxjs.fromEvent<Changes<IGuest>>(feed, "data"),
      // convert error events to errors.
      rxjs.fromEvent<RethinkDBError>(feed, "error").pipe(rxOperator.tap(err => { throw err; }))
    );

where Changes and RethinkDBError are from Rethinkdb-ts.

Now same thing is broken in v7.

fromEvent complains that it can't resolve either Changes<IGuest>> or RethinkDBerror.

Can someone please help me in resolving this? What is the correct use for fromEvent in server side coding?

[backbone87]

you should not set generic type parameters explicitly:

/** @deprecated Do not specify explicit type parameters. Signatures with type parameters that cannot be inferred will be removed in v8. */

you should remove them:

const event$ = rxjs.merge(
  rxjs.fromEvent(feed, "data"),
  // convert error events to errors.
  rxjs.fromEvent(feed, "error").pipe(rxOperator.tap(err => { throw err; }))
);

ofc this only works, if feed event listeners are properly typed with overloads for different events. if not, then you probably need to resort to a type cast:

const event$ = rxjs.merge(
  rxjs.fromEvent(feed, "data"),
  // convert error events to errors.
  rxjs.fromEvent(feed, "error").pipe(rxOperator.tap(err => { throw err; }))
) as Observable<Changes<IGuests>>;

[pratikgaikwadhive]

@backbone87,

Thank you for replying. changes comes from rethinkdb-ts which is completely written in TS. IGuest is from my internal project which is also written in TS. When I hover my mouse over feed it shows correct type. But let me try your second option

[backbone87]

from a quick look at rethinkdb-ts it seems like they just plainly extend EventEmitter without overloading its methods with proper event specific typing. you can test this very easily yourself:

feed.on('data', (...args) => {
  /* args should be properly typed here over your domain */
});

so I guess you must resort to typecasting the observable.

[cartant]

The type parameter was removed because it had no type-safe purpose. It was nothing more than a type assertion in disguise and type assertions are better represented using the proper syntax - as Observable<Changes<IGuests>> - as Oliver pointed out above.

[pratikgaikwadhive]

Thanks all, I will be using type casting for now.