如何通过方法创建可观察的rxjs

Question

I think I am trying to do something simple but I have had no luck in solving it. I want to create an observable that notifies its subscribers when the method of another object is called. I think an RxJS Observable is the right approach but I don't know how to create my Observable. I do not have access to modify the handle.ready function as it is in the DataLib library.

//Lets say I need to Observe the handle object for when it calls ready().
let handle = DataLib.getDataAsyncronously();
//sometime in the future DataLib will call handle.ready() which means that       
//the data is ready.
let myObservable = Rx.Observable.XXXXXX(handle.ready() is called);
myObservable.subscribe(()=>{
   //handle.ready() method just got called.
   //Do something now that handle.ready() has been called by DataLib.
});

How would I create myObservable such that subscribers are notified when handle.ready() gets called?

Answer 1

The only way to attach to handle would be to handle.ready() seems to replace it..?

Typically library APIs would be more like this

DataLib.handleDataAsyncronously(handler);

or have the shape of an event emitter (onReady()) than like this:

let handle = DataLib.getDataAsyncronously();

I will just assume your library does have an API precisely as you have described here rather than you maybe oversimplified it's API.

The implementation remains simple. Making a number of assumptions, including that the original handle.ready() still needs to be called, I would write something like this:

const originalHandler = handle.ready.bind(handle);
const ready$ = new Rx.Subject();
handle.ready = () => {
   originalHandler();
   ready$.onNext(true);
}

ready$
  .switchMap(Rx.Observable.from(handle.generatedValues)) // I assume this happens?
  .subscribe((handleValue) => {
   // handle.ready() method just got called.
   // Do something now that handle.ready() has been called by DataLib.
   // Or work with handleValue
});

If your library would at least return an event emitter, you could do something beautiful like:

const ready$ = Rx.Observable.fromEvent(handle, 'ready');