Using Object.defineProperty to fake an Array-like object that can be iterated over with a for loop or Array.prototype.slice.

enumerable.js

function Enumerable(generator, length, start) {
  this.generator = generator;
  this.length = length || Infinity;
  this.current = start || 0;
  this.index = 0;
	Object.defineProperty(this, this.index, { get: this.next, configurable: true });
}

Enumerable.prototype.next = function() {
  if (this.index < this.length) {
    Object.defineProperty(this, this.index, { value: this.current });
    Object.defineProperty(this, this.index + 1, { get: this.next, configurable: true });
    this.index = this.index + 1;
    this.current = this.generator(this.current);
  }
  return this.current;
}