<main>
 <div class="cd-index cd-main-content">
  <div>
   <h1>Page Transition</h1>
   <!-- your content here -->
  </div>
 </div>
</main>
 
<div class="cd-cover-layer"></div> <!-- this is the cover layer -->
 
<div class="cd-loading-bar"></div> <!-- this is the loading bar -->      

body::after, body::before {
 /* these are the 2 half blocks which cover the content once the animation is triggered */
 height: 50vh;
 width: 100%;
 position: fixed;
 left: 0;
}
body::before {
 top: 0;
 transform: translateY(-100%);
}
body::after {
 bottom: 0;
 transform: translateY(100%);
}
body.page-is-changing::after, body.page-is-changing::before {
 transform: translateY(0);
}       

.cd-loading-bar {
 /* this is the loading bar - visible while switching from one page to the following one */
 position: fixed;
 height: 2px;
 width: 90%;
}
.cd-loading-bar::before {
 /* this is the progress bar inside the loading bar */
 position: absolute;
 left: 0;
 top: 0;
 height: 100%;
 width: 100%;
 transform: scaleX(0);
 transform-origin: left center;
}
.page-is-changing .cd-loading-bar::before {
 transform: scaleX(1);
}       

$('main').on('click', '[data-type="page-transition"]', function(event){
  event.preventDefault();
  //detect which page has been selected
  var newPage = $(this).attr('href');
  //if the page is not animating - trigger animation
  if( !isAnimating ) changePage(newPage, true);
});        

function changePage(url, bool) {
  isAnimating = true;
  // trigger page animation
  $('body').addClass('page-is-changing');
  //...
  loadNewContent(url, bool);
  //...
}        

function loadNewContent(url, bool) {
  var newSectionName = 'cd-'+url.replace('.html', ''),
   section = $('<div class="cd-main-content '+newSectionName+'"></div>');
    
  section.load(url+' .cd-main-content > *', function(event){
   // load new content and replace <main> content with the new one
    $('main').html(section);
    //...
    $('body').removeClass('page-is-changing');
    //...
 
    if(url != window.location){
     //add the new page to the window.history
     window.history.pushState({path: url},'',url);
    }
 });
}        

$(window).on('popstate', function() {
  var newPageArray = location.pathname.split('/'),
    //this is the url of the page to be loaded 
    newPage = newPageArray[newPageArray.length - 1];
  if( !isAnimating ) changePage(newPage);
});