Custom Iterator

const range = {
  start: 1,
  end: 5,

  [Symbol.iterator]() {
    this.current = this.start;
    return this;
  },

  next() {
    if (this.current <= this.end) {
      return { done: false, value: this.current++ };
    } else {
      return { done: true };
    }
  }
};