Creating an Observable from scratch

observable-from-scratch

function Observer(destination) {
  this.destination = destination
}

Observer.prototype = {
  constructor: Observer,

  next(value) {
    if (this.destination.next && !this.isUnsubscribed) {
      this.destination.next && this.destination.next(value)
    }
  },

  error(e) {
    if (!this.isUnsubscribed) {
      if (this.destination.error) {
        this.destination.error(e)
      }
      this.unsubscribe()
    }
  },

  complete() {
    if (!this.isUnsubscribed) {
      if (this.destination.complete) {
        this.destination.complete()
      }
      this.unsubscribe()
    }
  },

  unsubscribe() {
    this.isUnsubscribed = true
    if (this._unsubscribe) {
      this._unsubscribe()
    }
  }
}

function Observable(_subscribe) {
  this._subscribe = _subscribe
}

Observable.prototype = {
  constructor: Observable,

  subscribe(subscriber) {
    const observer = new Observer(subscriber)
    observer._unsubscribe = this._subscribe(observer)
    return _ => observer.unsubscribe()
  }
}

const a = [
  'Fred', 
  'Quentin', 
  'idiot', 
  'Doug', 
  'tr0n', 
  'James', 
  'Bitchface', 
  'Maude',
  'Gladys',
  'Ploppy',
  'Manuel',
  'Greg'
]

const observable$ = new Observable((observer) => {
  let i = 0
  const id = setInterval(() => {
    if (i < a.length) {
      observer.next(`Sup ${a[i]}`)
      i++
    } else {
      observer.complete()
    }
  }, 100)
  
  return () => {
    console.log('Are you sure you want to unsubscribe? Kidding, unsubscribed.')
    clearInterval(id)
  }
})

const observer = {
  next(x) { console.log('next -> ' + x)},
  error(err) {},
  complete() { console.log('We are done diddly done!')}
}

const subscription$ = observable$.subscribe(observer)