The oncomplete event handler of the IDBTransaction interface handles the complete event, fired when the transaction successfully completes.

As of Firefox 40, IndexedDB transactions have relaxed durability guarantees to increase performance (see bug 1112702), which is the same behaviour as other IndexedDB-supporting browsers. Previously in a readwrite transaction IDBTransaction.oncomplete was fired only when all data was guaranteed to have been flushed to disk. In Firefox 40+ the complete event is fired after the OS has been told to write the data but potentially before that data has actually been flushed to disk. The complete event may thus be delivered quicker than before, however, there exists a small chance that the entire transaction will be lost if the OS crashes or there is a loss of system power before the data is flushed to disk. Since such catastrophic events are rare most consumers should not need to concern themselves further.

Note: This feature is available in Web Workers.

Note: In Firefox, if you wish to ensure durability for some reason (e.g. you're storing critical data that cannot be recomputed later) you can force a transaction to flush to disk before delivering the complete event by creating a transaction using the experimental (non-standard) readwriteflush mode (see IDBDatabase.transaction.) This is currently experimental, and can only be used if the dom.indexedDB.experimental pref is set to true in about:config.


transaction.oncomplete = function() { ... };


In the following code snippet, we open a read/write transaction on our database and add some data to an object store. Note also the functions attached to transaction event handlers to report on the outcome of the transaction opening in the event of success or failure. Note the transaction.oncomplete = function(event) { }; block, which reports back when the transaction was successful. For a full working example, see our To-do Notifications app (view example live.)

// Let us open our database
var DBOpenRequest ="toDoList", 4);

DBOpenRequest.onsuccess = function(event) {
  note.innerHTML += '<li>Database initialised.</li>';
  // store the result of opening the database in the db variable. This is used a lot below
  db = DBOpenRequest.result;
  // Run the addData() function to add the data to the database

function addData() {
  // Create a new object ready for being inserted into the IDB
  var newItem = [ { taskTitle: "Walk dog", hours: 19, minutes: 30, day: 24, month: "December", year: 2013, notified: "no" } ];

  // open a read/write db transaction, ready for adding the data
  var transaction = db.transaction(["toDoList"], "readwrite");

  // report on the success of opening the transaction
  transaction.oncomplete = function(event) {
    note.innerHTML += '<li>Transaction completed: database modification finished.</li>';

  transaction.onerror = function(event) {
    note.innerHTML += '<li>Transaction not opened due to error: ' + transaction.error + '</li>';

  // create an object store on the transaction
  var objectStore = transaction.objectStore("toDoList");

  // add our newItem object to the object store
  var objectStoreRequest = objectStore.add(newItem[0]);

  objectStoreRequest.onsuccess = function(event) {
    // report the success of our new item going into the database
    note.innerHTML += '<li>New item added to database.</li>';


Specification Status Comment
Indexed Database API
The definition of 'oncomplete' in that specification.
Editor's Draft  

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support 23webkit
10 moz
16.0 (16.0)
10, partial 15 7.1
Available in workers (Yes) 37.0 (37.0) ? (Yes) ?
Feature Android Firefox Mobile (Gecko) Firefox OS IE Phone Opera Mobile Safari Mobile
Basic support 4.4 22.0 (22.0) 1.0.1 10 22 8
Available in workers (Yes) 37.0 (37.0) (Yes) ? (Yes) ?

See also

Document Tags and Contributors

 Contributors to this page: jpmedley, chrisdavidmills, fscholz
 Last updated by: jpmedley,