Vanilla Javascript Page Loader

script.js

// Page Loader
document.addEventListener('readystatechange', function(event) {
  if (document.readyState === "complete") {
    setTimeout(function(){
      document.getElementById('loader').classList.add('hide');
    }, 1000);
  }
});

window.addEventListener( 'beforeunload', function( event ) {
  event.preventDefault();
  document.getElementById('loader').classList.remove('hide');
  console.log(event);
});