Call Back

HTML

<ul id="posts"></ul>

JavaScript

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

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

function createPost(post, callback) {
  setTimeout(() => {
    posts.push(post);
    callback();
  }, 2000);
}

createPost({ title: 'Post Three', body: 'This is post three' }, getPosts);

Code from Brad Traversy's tutorial:
Async JS Crash Course - Callbacks, Promises, Async Await
https://www.youtube.com/watch?v=PoRJizFvM7s

Call Back

HTML

JavaScript

Demo