generators-laziness.js

const lessThan = function(end, value) {
  return function(value) {
    return value < end;
  };
}

// 25 alphabet character letters
const lessThan26 = lessThan(26);

const lazyMap = function* (iterable, callback) {
  for (let value of iterable) {
    yield callback.call(this, value);
  }
};

const numberToAlphabet = function(value) {
  //97 in ASCII is 'a'
  //Our min value is 1
  return String.fromCharCode(96 + value);
 };

const numbers = [...randomNumberGenerator(10)];
console.log(numbers);
//[ 74, 16, 74, 24, 54, 96, 1, 71, 71, 77 ]

//Our chained generator object
let alphabebtCharIterator = lazyMap(filter(numbers), lessThan26), numberToAlphabet);

alphabetCharIterator.next();
//{ value: 'o', done: false }

alphabetCharIterator.next();
//{ value: 'w', done: false }

alphabetCharIterator.next();
//...