title: Check if IndexedDB objectStore already contains key
body: <p>Adding an object to an IndexedDB objectStore will fail if the key already exists. How can I check for the existence of an object with a given key – preferably synchronously (no reason for another layer of callbacks) and without pulling the object.</p>
  
  <p>I know how to do get requests asynchronously via transactions, but it seems a bit of an ordeal to go through every time I want to add an object.</p>
  
  <p><em>note</em> Solution only has to work in Chrome (if that helps)</p>