Promise races

promise-races-second.js

const $page = document.getElementById('page')
let currentPage = 'no-page'

const setPage = title => {
  if (currentPage !== title) return;
  $page.innerText = title
}

const loadPage = (title, time) =>
  new Promise(resolve => 
    setTimeout(() => resolve(title), time)
  )
  
const onClickChangePage = button =>
  button.addEventListener('click', () => {
    const nextPage = button.getAttribute('data-page')
    const delay = +button.getAttribute('data-delay')
    
    currentPage = nextPage
    
    loadPage(nextPage, delay)
      .then(setPage)
  })

Array.from(document.getElementsByTagName('button'))
  .map(onClickChangePage)