const Observable = function(producer) {

  this.subscribe = producer

}

​

Observable.fromPromise = function(promise){

  const producer = observer => {

​

    promise

      // call observer.next once the promise resolve

      .then(value => {

        observer.next(value)

        // signaling completion

        observer.complete()

      })

      // handling errors

      .catch(reason => {

        observer.error(reason)

        observer.complete()

      })

  }

​

  //create and return a new observable

  return new Observable(producer)

}

​

​

const request = fetch('https://null.jsbin.com')

const observable = Observable.fromPromise(request)

​

observable.subscribe({

  next(value){console.log(value.status)},

  complete(){console.log('done')},

  error(err){console.log(err)}

})