Odd Tens Observable

by gladtocode

HTML

<body>
  Values:
</body>

JavaScript

const print = (value) => {
  const paragraph = document.createElement('p');
  paragraph.innerHTML = value;
  document.body.appendChild(paragraph);
}

const integerObservable = (observer) => {
  let x = 0;
  setInterval(
    () => {
      x = x + 1;
      observer(x);
    },
    500
  );
};

const ignoreEvenOperator = (originalObservable) => {
  return (observer) => {
    originalObservable((originalValue) => {
      if (originalValue % 2 == 1) {
        // Only emit the value if it is odd
        observer(originalValue);
      }
    });
  }
}
const multiplyOperator = (originalObservable, multiplier) => {
  return function(observer) {
    // Our internalObserver observes the original stream, and for each
    // value emitted, we emit a corresponding value -- the original value
    // multipled by the specified multplier
    const internalObserver = (value) => observer(value * multiplier);
    originalObservable(internalObserver);
  }
}

class Observable {
  constructor(observableFunction) {
    this.observableFunction = observableFunction;
    this.subscribe = this.subscribe.bind(this);
  }
  
  subscribe(observer) {
    return this.observableFunction(observer);
  }
  
  multiply(multiplier) {
    return new Observable(multiplyOperator(this.observableFunction, multiplier));
  }
  
  ignoreEven() {
    return new Observable(ignoreEvenOperator(this.observableFunction));
  }
}

const observable = new Observable(integerObservable)
observable.ignoreEven().multiply(10).subscribe(print);