Async code execution with generators

async-execution-with-generators.js

const isPromise = fn => fn && fn.then;

const getUser = () => new Promise((resolve, reject) => {
  setTimeout(()=> {
    resolve({name: 'John Lavoier'});
  }, 2000);
});

const getProfile = () => new Promise((resolve, reject) => {
  setTimeout(()=> {
    resolve({job: 'JavaScript Programmer', city: 'Ribeirão Preto'});
  }, 4000);
});

const runAsyncCode = (fn) => {
  const gen = fn();
  let nextValue;
  
  const next = (nextParam) => {
    nextValue = nextParam ? gen.next(nextParam) : gen.next(); 
    
    if(!nextValue.done) {
      if(isPromise(nextValue.value)) {
        nextValue.value.then(v => next(v));
      } else {
        next(nextValue.value);
      }
    }
  }
  next();
}

function* asyncCalls() {
  const randomValue = yield "just a random value";
  console.log('print random', randomValue);
  
  const user = yield getUser();
  console.log(`the user name is ${user.name}`);
  
  const profile = yield getProfile();
  console.log(`user job: ${profile.job}, user city: ${profile.city}`);
}

runAsyncCode(asyncCalls);