Exemplo simples de Custom Event

custom_event.js

var event = new CustomEvent('build', { 
  'detail': 'wescley'
});

document.addEventListener('build', function(e){
  alert(e.detail);
  var nome = e.detail + ' matos';
  var ajaxEvent = new CustomEvent('ajax-return', {
    'detail': nome
  });
  
  document.dispatchEvent(ajaxEvent);
});

document.addEventListener('ajax-return', function(e){
  alert(e.detail);
});

document.dispatchEvent(event);