promises.js

const posts = [
  { title: 'Post One', body: 'This is post one' },
  { title: 'Post Two', body: 'This is post two' },
];

function getPosts() {
  setTimeout(function () {
    let output = '';
    posts.forEach(function (post, index) {
      output += `<li>${post.title}</li>`;
    });
    document.body.innerHTML = output;
  }, 1000);
}

function createPost(post) {
  return new Promise((resolve, reject) => {
    setTimeout(function () {
      posts.push(post);

      const error = false;

      if (!error) {
        resolve();
      } else {
        reject('Error: Something went wrong');
      }
    }, 2000);
  });
}

createPost({ title: 'Post Three', body: 'This is post three' })
  .then(getPosts)
  .catch(err => console.log(err));

// Async / Await
async function init() {
  await createPost({ title: 'Post Three', body: 'This is post three' });

  getPosts();
}

init();

// Async await with fetch
async function fetchUsers() {
  const res = await fetch('https://jsonplaceholder.typicode.com/users');

  const data = await res.json();
  console.log(data);
}
fetchUsers();

// Promise.all
const promise1 = Promise.resolve('Hello World');
const promise2 = 10;
const promise3 = new Promise((resolve, reject) =>
  setTimeout(resolve, 2000, 'GoodBye')
);
const promise4 = fetch('https://jsonplaceholder.typicode.com/users').then(res =>
  res.json()
);

Promise.all([promise1, promise2, promise3, promise4]).then(values =>
  console.log(values)
);