fromPromise

연산자(operator) 정의: fromPromise(promise: Promise, scheduler: Scheduler): Observable

Create observable from promise, emitting result.

Flattening operators can generally accept promises without wrapping!

You could also use Observable.from for the same result!

Examples

Example 1: Converting promise to observable and catching errors

( jsBin | jsFiddle )

//example promise that will resolve or reject based on input
const myPromise = (willReject) => {
    return new Promise((resolve, reject) => {
          if(willReject){
            reject('Rejected!');
        }
        resolve('Resolved!');
    })
}
//emit true, then false
const source = Rx.Observable.of(true, false);
const example = source
    .mergeMap(val => Rx.Observable
        //turn promise into observable
        .fromPromise(myPromise(val))
        //catch and gracefully handle rejections
        .catch(error => Rx.Observable.of(`Error: ${error}`))
    )
//output: 'Error: Rejected!', 'Resolved!'
const subscribe = example.subscribe(val => console.log(val));

Additional Resources

• fromPromise - Official docs
• Creation operators: from, fromArray, fromPromise - André Staltz
• fromPromise - Guide

Source Code: https://github.com/ReactiveX/rxjs/blob/master/src/observable/PromiseObservable.ts