function generator() {
  var i = 0, j = 1, limit = 100;
  while (j <= limit) {
    yield j;
    [i, j] = [j, i+j];
  }
}
var geniter = generator();
for (var item in geniter) {
  alert(item); // => 1,1,2,3,5,8,13,21,34,55,89
}