//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));

​