//emit array as a sequence

const source = Rx.Observable.from([1,2,3,4,5]);

//pass in your own function to add operators to observable

const obsArrayPlusYourOperators = (yourAppliedOperators) => {

  return source

    .map(val => val + 1)

    .let(yourAppliedOperators)

 };

const addTenThenTwenty = obs => obs.map(val => val + 10).map(val => val + 20);

const subscribe = obsArrayPlusYourOperators(addTenThenTwenty)

    //output: 32, 33, 34, 35, 36

    .subscribe(val => console.log('let FROM FUNCTION:', val));