generator idea

gistfile1.js

var generator = function (fn) {

  var next_callback  = null,
      yield_callback = null,
      yield_value    = null;

  var reset = function () {
    next_callback  = null;
    yield_callback = null;
    yield_value    = null;
  }

  var next = function (cb) {
    if (yield_callback !== null) {
      var v = yield_value,
          c = yield_callback;
      reset(); c(); cb();
    } else {
      next_callback = cb;
    }
  };

  var yield = function (val, cb) {
    if (next_callback !== null) {
      var c = next_callback;
      reset(); c(val); cb();
    } else {
      yield_callback = cb;
      yield_value = val;
    }
  };

  fn(yield);

  return { next: next };
};

var loop = function (fn) {
  var recur = function () { fn(next); }
  var next  = function () { setTimeout(recur, 0); };
  recur();
}

var g = generator(function (yield) {
  var count = 0;
  loop(function (next) {
    count++;
    setTimeout(function () {
      yield(123, next);
    }, count * 100);
  });
});

loop(function (next) {
  g.next(function (val) {
    console.log(val);
    next();
  });
});