github-birthday.js

async function getData(event) {
  event.preventDefault();
  document.querySelector('.output').classList.add('visible');

  let createdDate;
  let data = [];
  const user = document.getElementById('username').value;

  await fetch(`https://api.github.com/users/${user}`)
    .then(response => response.json())
    .then(response => (createdDate = response.created_at));

  const createdDay = new Date(createdDate).getMonth();
  const createdMonth = new Date(createdDate).getDate();