IDBRequest.transaction

var myTransaction = request.transaction;

var title = "Walk dog";

// Open up a transaction as usual
var objectStore = db.transaction(['toDoList'], "readwrite").objectStore('toDoList');

// Get the to-do list object that has this title as it's title
var objectStoreTitleRequest = objectStore.get(title);

objectStoreTitleRequest.onsuccess = function() {
  // Grab the data object returned as the result
  var data = objectStoreTitleRequest.result;

  // Update the notified value in the object to "yes"
  data.notified = "yes";

  // Create another request that inserts the item back
  // into the database
  var updateTitleRequest = objectStore.put(data);

  // Log the transaction that originated this request
  console.log("The transaction that originated this request is " + updateTitleRequest.transaction);

  // When this new request succeeds, run the displayData()
  // function again to update the display
  updateTitleRequest.onsuccess = function() {
    displayData();
  };
};

var openRequest = indexedDB.open('db', 2);
console.log(openRequest.transaction); // Will log "null".

openRequest.onupgradeneeded = function(event) {
  console.log(openRequest.transaction.mode); // Will log "versionchange".
  var db = openRequest.result;
  if (event.oldVersion < 1) {
    // New database, create "books" object store.
    db.createObjectStore('books');
  }
  if (event.oldVersion < 2) {
    // Upgrading from v1 database: add index on "title" to "books" store.
    var bookStore = openRequest.transaction.objectStore('books');
    bookStore.createIndex('by_title', 'title');
  }
};

openRequest.onsuccess = function() {
  console.log(openRequest.transaction); // Will log "null".
};