title: cannot set onsuccess callback for indexeddb add transaction
body: <p>i get a problem to set the callback function before indexeddb add transaction</p>
  
  <pre><code>os = ...the object store (IDBObjectStore) object assigned here
  os.onsuccess = function(){alert('dont mess with Messi')}
  os.add({name:'Lionel Messi',team:'FC Barcelona',position:'striker',number:10});
  </code></pre>
  
  <p>the entry was successfully added to the object store, but the function on onsuccess event won't fired. there's another event called onerror. should i use it instead? i dont think so</p>
  
  <p>don't ask me for 'can you give the error part?' because there's no error at all</p>