title: PWA - Fetch GET URL when online
body: <p>I am a bit confused about approaching deferred fetch requests. </p>
  
  <p>I have a button in my app. when clicked, I want it to perform a fetch using the GET method. If the device is offline, I want that fetch deferred until the the device is online again. The fetch can complete successfully now or anytime in the future.</p>
  
  <p>What approach should I be taking? 
  Can you also clarify where the deferment should be take place? i.e. app script or service worker</p>