reactivex_button_demo_observable_fromPromises.js

//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));