How to make Observable from callback

Question

I need to make observable from

window.web3.eth.getCoinbase((error, result) => { ... });

Is it a good idea?

new Observable<string>(o => {
    this.w.eth.getCoinbase((err, result) => {
        o.next(result);
        o.complete();
    });
});

Doyon

I'm not familiar with the first half, but you can certainly do what you are doing unless it's triggered by an event? If that is true you can use fromEvent() – Stiver

You can do this, but I’m not sure if there’s a reason to. You’re not going to get multiple values back from getCoinbase. The callback is only fired once (The API switched to Promise in web3 1.0.0). – Minnesinger

It's usually a good idea to use the built-in observable creators wherever possible. Look at bindNodeCallback. – Leann

Answer 1

RxJS includes a bindNodeCallback observable creator specifically for creating observables from async functions that use Node-style callbacks.

You could use it like this:

const getCoinbaseAsObservable = Observable.bindNodeCallback(
  callback => this.w.eth.getCoinbase(callback)
);

let coinbaseObservable = getCoinbaseAsObservable();
coinbaseObservable.subscribe(
  result => { /* do something with the result */ },
  error => { /* do something with the error */ }
);

Note that an arrow function is used to ensure the getCoinbase method is called using this.w.eth as its context.

Leann