Iterators basic example.

iterator.js

function makeIterator(){
    var nextIndex = 0;
    return {
       next: function(){
           return  nextIndex < 5 ? { value: nextIndex++, done: false} : {done: true}
       }
    }
}

var it = makeIterator();
console.log('Value: '+ it.next().value);
console.log('Value: '+ it.next().value); 
console.log('Done: ' + it.next().done);  
console.log('Value: '+ it.next().value);
console.log('Value: '+ it.next().value);
console.log('Value: '+ it.next().value);
console.log('Done: ' + it.next().done); 

//https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Iterators_and_Generators#Generators