fibo-gen3.js

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

GenIter.prototype.next = function next() {
  var f = this.genf;
  var result = f(this.c);
  if (result === stop) {
    return {done: true};
  } else {
    return {done: false, value: result};
  }
}