functional-programming.js

const Observable = require('./observer');
const Iterator = require('./iterator');

const observer = new Observable();
const iterator = new Iterator();

observer.subscribe((data)=>{
    console.log("Listener 1", data);
    console.log("");
})

observer.subscribe((data)=>{
    console.log("Listener 2", data);
    console.log("");
})

iterator.add(`Hello ${Math.random()}`);
iterator.add(`Hello ${Math.random()}`);
iterator.add(`Hello ${Math.random()}`);
iterator.add(`Hello ${Math.random()}`);
iterator.add(`Hello ${Math.random()}`);
iterator.add(`Hello ${Math.random()}`);
setInterval(()=>{
    const result = iterator.next();
    if(result !== -1){
        observer.emit(result);
    }else{
        console.log('there is no contain data');
    }
},1000);

iterator.js

module.exports = class Iterator {
    constructor(){
        this.data = [];
        this.currentIndex = 0;
    }
    add(data){
        this.data.push(data);
    }
    hasNext(){
        return this.currentIndex === this.data.length;
    }
    next(){
        if(!this.hasNext()){
            const result = this.data[this.currentIndex];
            this.currentIndex++;
            return result;
        }
        return -1;
    }
}

observer.js

module.exports = class Observable {
    constructor(){
        this.listObservers = [];
    }

    subscribe(func){
        this.listObservers.push(func);
    }

    emit(data){
        this.listObservers.forEach((func)=> func(data));
    }
    
    unsubscribe(func){
        this.listObservers = this.listObservers.filter((observFunction)=> observFunction !== func);
    }
}