title: Why is the method of an Object stored to chrome.storage.sync not a function when retrieved?
body: <p>I'm storing a Timer object into <code>chrome.storage.sync</code>. When I retrieve the Timer object and try to call one of its methods, <code>countdown()</code>, the method no longer exists: </p>
  
  <pre><code>  let clock = new Timer(1);
    let key = "myKey";
    chrome.storage.sync.set({[key]: clock});
    chrome.storage.sync.get(key, function(items){
      items[key].countdown();
    });
  </code></pre>
  
  <p>Chrome devTools says: "Error in response to storage.get: TypeError: items[key].countdown is not a function." </p>