CODEWITHSUNDEEP
javascripttypescriptrxjsobservable
hyperdrive
hyperdrive

Reputation: 1846

Wrapping event handler callback in Observable

I'm trying to find a pattern for wrapping an event callback from a library to an RxJS Observable.

The library I'm using registers handlers for events like this:

const someHandler = (args) => {}`;
const resultCallback = (result) => {}`;

Library.addHandler('SOME_EVENT', someHandler, resultCallback);
Library.removeHandler('SOME_EVENT', someHandler, resultCallback);

The resultCallback is a callback that returns if the handler was registered successfully.

Ideally, I would like to pass the handler in as a parameter of the function, and emit it's result.

I don't know how I can emit the value of the handler from this function, while also maintaining an object reference to the handler for removal.

addEventHandlerObservable<T>(handler: any): Observable<T> {

    return new Observale(observer => {

        SomeLibrary.addHandler('SOME_EVENT', handler,
        (result) => { 
            // was registered successfully?
            if(result.failed) {
                observer.error();
                observer.complete();
            }
        });

    });

}

Upvotes: 1

Views: 895

Answers (1)

bryan60
bryan60

Reputation: 29325

rxjs already did this for you, with the fromEventPattern observable. 

const resultCallback = (result) => {}; // not hyper clear on the point of this

const events$ = fromEventPattern(
  (handler) => Library.addHandler('SOME_EVENT', handler, resultCallback),
  (handler) => Library.removeHandler('SOME_EVENT', handler, resultCallback);
);

you don't "pass in" the handler here. Your subscribe IS your handler:

events$.subscribe((val) => someHandler(val));

Upvotes: 2

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