// custom error handling logic

const retryThreeTimes = obs => obs.retry(3).catch(_ => Rx.Observable.of('ERROR!'));

const examplePromise = val => new Promise(resolve => resolve(`Complete: ${val}`));

​

//faking request

const subscribe = Rx.Observable

    .of('some_url')

  .mergeMap(url => examplePromise(url))

  // could reuse error handling logic in multiple places with let

  .let(retryThreeTimes)

  //output: Complete: some_url

  .subscribe(result => console.log(result));

​

const customizableRetry = retryTimes => obs => obs.retry(retryTimes).catch(_ => Rx.Observable.of('ERROR!'));

​

//faking request

const secondSubscribe = Rx.Observable

    .of('some_url')

  .mergeMap(url => examplePromise(url))

  // could reuse error handling logic in multiple places with let

  .let(customizableRetry(3))

  //output: Complete: some_url

  .subscribe(result => console.log(result));