//emit 'Hello' and 'Goodbye'

const source = Rx.Observable.of('Hello', 'Goodbye');

//example with promise

const examplePromise = val => new Promise(resolve => resolve(`${val} World!`));

// map value from source into inner observable, when complete emit result and move to next

const example = source.concatMap(val => examplePromise(val))

//output: 'Example w/ Promise: 'Hello World', Example w/ Promise: 'Goodbye World'

const subscribe = example.subscribe(val => console.log('Example w/ Promise:', val));