// http://nick.balestra.ch/2016/Understanding-the-observable-type/

const Observable = function(producer) {

  this.subscribe = producer

}

​

// http://nick.balestra.ch/2016/creating-observables/

Observable.of = function(...values){

  const producer = observer => {

    try {

      values.forEach(value => observer.next(value))

      observer.complete()

    } catch(err) {

      observer.error(err)

    }

  }

​

  return new Observable(producer)

}

​

​

Observable.prototype.map = function(transformation){

  const originalProducer = this.subscribe;

​

  const newProducer = function(observer){

    originalProducer({

      next (value) {observer.next(transformation(value))},

      error (err) {observer.error(err)},

      complete () {observer.complete()}

    })

  }

​

  return new Observable(newProducer)

}

​

​

const three = Observable.of(3)

const square = (num) => num * num

​

const nine = three.map(square)

​

nine.subscribe({

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

  error(err) { console.log('Error: ', err) },

  complete() { console.log('Done') }

})

​