https://medium.com/p/d9662a2847fe/edit

Concurrency.js

const API = 'https://jsonplaceholder.typicode.com';


// Data Fetching and Logic
const getData = (endpoint) => 
  fetch(`${API}/${endpoint}`)
    .then(resp => resp.json());

const findUserByUserName = (username) => 
  getData(`users?username=${username}`)
    .then(users => users[0]);
const getPostsUser = (userId) => getData(`posts?userId=${userId}`); 

const getPostsByUserName = (username) => 
  findUserByUserName(username)
    .then(user => getPostsUser(user.id));


//Execution
console.log('Application Starts');
console.log('------------------');
console.log('Posts from Bret are');
const postsPromise = getPostsByUserName('Bret');
postsPromise.then(posts => {
  posts.forEach((post, i) => console.log(`${i}. ${post.title}`));  
});
console.log('Application Finishes');