blah.js

var fn = function* (args) {
  yield asyncFn(args);
};

Object.defineProperty(this, 'fn', {
  get: function () {
    return function () {
      return fn.next();
    }
  }
});

var value = fn(1);

blah2.js

function autoGen(fn) {
  return function () {
    return fn.next();
  }
}

var fn = autoGen(function* (args) {
  yield asyncFn(args);
};

var value = fn(1);