function* nTimesTable(n) {
  for(var i = 1; i <= 9; i++) yield n * i;
}

var nineTimesTable = nTimesTable(9);

var result = nineTimesTable.next();
console.log(result); // { value: 9, done: false }
result = nineTimesTable.next();
console.log(result); // { value: 18, done: false }
result = nineTimesTable.next();
console.log(result); // { value: 27, done: false }

// keep calling...

result = nineTimesTable.next();
console.log(result); // { value: 72, done: false }
result = nineTimesTable.next();
console.log(result); // { value: 81, done: false }
result = nineTimesTable.next();
console.log(result); // { value: undefined, done: true }

function caller(iter) {
  var result, value;
  while(result = iter.next()) {
    if(result.done) break;
    value = result.value || value;
  }
  return value;
}

var result = caller(nTimesTable(3));
console.log(result); // 27

function * nTimesTable(n) {
  for(var i = 1; i <= 9; i++) yield { n: n, i: i, result: n * i };
}

function caller(iter, func) {
  var result, value;
  while(result = iter.next()) {
    if(result.done) break;
    value = result.value || value;
    if(func) func(value);
  }
  return value;
}

caller(nTimesTable(3), value => {
  console.log('%d x %d = %d', value.n, value.i, value.result);
});

function* getAnimalInCage() {
  yield "Wombat";
  yield "Koala";
  return "Kangaroo";
}

function* Cage() {
  var cageAnimals = getAnimalInCage();

  var first = yield cageAnimals;
  var second = yield cageAnimals;
  var third = yield cageAnimals;

  console.log(first, second, third);
}

var cage = Cage();
var firstStop = cage.next();
// {value: iterator, done: false}

var firstAnimal = firstStop.value.next();
// firstAnimal: {value: "Wombat", done: false}
var secondStop = cage.next(firstAnimal.value);

var secondAnimal = secondStop.value.next();
// secondAnimal: { value: 'Koala', done: false }

var thirdStop = cage.next(secondAnimal.value);
var thirdAnimal = thirdStop.value.next();
// thirdAnimal: { value: 'Kangaroo', done: true }

var lastStop = cage.next(thirdAnimal.value);

// Wombat Koala Kangaroo

function catchEscapedAnimal() {
  return function(done) {
    setTimeout(function() {
      done(null, {name: 'Kuma', type: 'Bear'});
    }, 1000);
  };
}

function* getTodaysZookeeper() {
  yield {status: 'loading'};
  return {status: 'loaded', name: 'Edward'};
}

function* Zoo() {
  var animal = yield catchEscapedAnimal();
  var zookeeper = yield getTodaysZookeeper();

  console.log('%s catches by %s', animal.name, zookeeper.name);
}

function compose(iter, value, next) {
  var result = iter.next(value);
  if(result.done) return next ? next(value) : value;
  else if(typeof result.value == 'function') {
    return result.value(function(err, data) {
      if(err) throw err;
      compose(iter, data);
    });
  } else if(typeof result.value.next == 'function') {
    var _iter = iter;
    next = function(result){
      compose(_iter, result);
    };
    iter = result.value;
    result = iter.next();
  }
  return compose(iter, result.value, next);
}

compose(Zoo());
// Kuma catches by Edward

var co = require('co');
co(Zoo());
// Kuma catches by Edward

$ npm install --save koa

var koa = require('koa');
var app = koa();

app.use(function* () {
  this.body = {"message": "Hello World"};
});

app.listen(3000);

var koa = require('koa');
var app = koa();

function catchEscapedAnimal() {
  return function(done) {
    setTimeout(function() {
      done(null, {name: 'Kuma', type: 'Bear'});
    }, 50);
  };
}

function* getTodaysZookeeper() {
  yield {status: 'loading'};
  return {status: 'loaded', name: 'Edward'};
}

function* Zoo() {
  var animal = yield catchEscapedAnimal();
  var zookeeper = yield getTodaysZookeeper();

  this.body = { message: animal.name + ' catches by ' + zookeeper.name };
}

app.use(Zoo);
app.listen(3000);

app.use(function* (next) {
  yield next;
  if(this.body) {
    this.body.ok = true;
  } else {
    this.body = { ok : false };
  }
});

app.use(function* (next) {
  var requestToken = this.request.get("Authorization");
  var accessToken = yield AccessTokensModel.findAccessTokenAsync(token);
  if(accessToken) {
    yield next;
  } else {
    this.body = { error: 'invalid_token' };
  }
});