use Generator and Promise to impelement async functions

generator_promise.js

function* getResponse() {
  yield new Promise(resolve => {
    request('example.com', res => {
      resolve();
    });
  });
  
  // you can have more functions. It's just a example. just do it
  // yield new Promise ....
}

const iterator = getResponse();
(function loop() {
  const next = iterator.next();
  if (next.done) {
    console.log('All functions is done');
    return;
  }
  
  next.value.then(loop);
}())