Javascript Number iterator(iterKeys)

/*/*from  w  w  w.ja v a 2 s  .c  om*/
 * JavaScript Number iterator
 * Requires JavaScript 1.7+
 *
 * 2010-03-11
 * 
 * By Eli Grey, http://eligrey.com
 *
 * Public Domain.
 * NO WARRANTY EXPRESSED OR IMPLIED. USE AT YOUR OWN RISK.
 */

"use strict";

Number.prototype.__iterator__ = function (iterKeys) {
 if (this % 1) {
  throw new TypeError("Integer expected for number iterator");
 }
 
 var i = 1 - iterKeys,
     j = this + i;
 
 if (j < 0) {
  i = j - i + iterKeys;
  j = +iterKeys;
 }
 
 for (; i < j; i++) {
  yield i;
 }
};

/* examples:
 * [i for (i in 5)] is [0,1,2,3,4]
 * [i for each (i in 5)] is [1,2,3,4,5]
 * [i for (i in -5)] is [-4,-3,-2,-1,0]
 * [i for each (i in -5)] is [-5,-4,-3,-2,-1]
 */