Mini CO

index.js

const log = function(args) {
  args = Array.isArray(args) ? args : Array.prototype.slice.call(arguments)
  console.log.apply(console, args);
};

const tOut = function(time) {
  return new Promise(function(resolve) {
    setTimeout(() => {
      resolve(time);
    }, time);
  });
};

const f = co(function *() {
  log('Ok');
  const t1 = yield tOut(1000);
  log('tOut1', t1);
  const t2 = yield tOut(2000);
  log('tOut2', 2000);
  return 666;
}).then(function(res) {
  log(res);
});

minico.js

function co(gen) {
  const ctx = this;
  const args = Array.prototype.slice.call(arguments, 1);

  return new Promise(function(resolve, reject) {
    gen = gen.apply(ctx, args);
    if (!gen || typeof gen.next !== 'function') return resolve(gen);

    onFulfilled();

    function onFulfilled(res) {
      let ret;
      try {
        ret = gen.next(res);
      } catch(e) {
        return reject(e);
      }

      next(ret);
      return null;
    }

    function onRejected(err) {
      let ret;
      try {
        ret = gen.throw(err);
      } catch(e) {
        return reject(e);
      }

      next(ret);
    }

    function next(ret) {
      if (ret.done) return resolve(ret.value);
      const value = ret.value;
      return value.then(onFulfilled, onRejected);
    }
  });
}