text: if('serviceWorker' in navigator){
  	navigator.serviceWorker.register('sw.js')
  		.then(reg => console.log('service worker registered'))
  		.catch(err => console.log('service worker not registered', err));
  }
  
  window.addEventListener('load', () => {
  	u('.btn').on('click', () => console.log('clicked') );
  });
  