fibo-gen2.js

function Context() {
  this.next = 0;
}

var stop = {};

Context.prototype.stop = function stop() {
  return stop;
}

function GenFun(c, genf) {
  this.c = c;
  this.genf = genf;
}

GenFun.prototype[Symbol.iterator] = function iterator() {
  return new GenIter(this.c, this.genf);
}

function wrap(genf) {
  var c = new Context();
  return new GenFun(c, genf);
}