IDBTransaction

The IDBTransaction interface of the IndexedDB API provides a static, asynchronous transaction on a database using event handler attributes. All reading and writing of data is done within transactions. You actually use IDBDatabase to start transactions and IDBTransaction to set the mode of the transaction (e.g. is it readonly or readwrite), and access an IDBObjectStore to make a request. You can also use it to abort transactions.

Note that as of Firefox 40, IndexedDB transactions have relaxed durability guarantees to increase performance (see bug 1112702.) 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.

If you must 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.

Note that transactions are started when the transaction is created, not when the first request is placed; for example consider this:

var trans1 = db.transaction("foo", "readwrite");
var trans2 = db.transaction("foo", "readwrite");
var objectStore2 = trans2.objectStore("foo")
var objectStore1 = trans1.objectStore("foo")
objectStore2.put("2", "key");
objectStore1.put("1", "key");

After the code is executed the object store should contain the value "2", since trans2 should run after trans1.

Transactions can fail for a fixed number of reasons, all of which (except the user agent crash) will trigger an abort callback:

• Abort due to bad requests, e.g. trying to add() the same key twice, or put() with the same index key with a uniqueness constraint. This causes an error on the request, which can bubble up to an error on the transaction, which aborts the transaction. Can be prevented by using preventDefault() on the error event on the request.
• Explicit abort() call from script
• Uncaught exception in request's success/error handler
• I/O error (actual failure to write to disk, e.g. disk detached, or other OS/hardware failure)
• Quota exceeded
• User agent crash

Properties

IDBTransaction.db Read only

The database connection with which this transaction is associated.

IDBTransaction.error Read only

Returns a DOMException indicating the type of error that occured when there is an unsuccessful transaction. This property is null if the transaction is not finished, is finished and successfully committed, or was aborted with IDBTransaction.abort function.

IDBTransaction.mode Read only

The mode for isolating access to data in the object stores that are in the scope of the transaction. For possible values, see the Constants section below. The default value is readonly.

IDBTransaction.objectStoreNames Read only

Returns a DOMStringList of the names of IDBObjectStore objects.

Event handlers

IDBTransaction.onabort Read only

The event handler for the abort event, fired when the transaction is aborted. This can happen due to:

• bad requests, e.g. trying to add() the same key twice, or put() with the same index key with a uniqueness constraint and there is no error handler on the request to call preventDefault() on the event,
• an explicit abort() call from script
• uncaught exception in request's success/error handler,
• an I/O error (actual failure to write to disk, e.g. disk detached, or other OS/hardware failure), or
• quota exceeded.

IDBTransaction.oncomplete Read only

The event handler for the complete event, thrown when the transaction completes successfully.

IDBTransaction.onerror Read only

The event handler for the error event, thrown when the transaction fails to complete.

Methods

Inherits from: EventTarget

IDBTransaction.abort

Rolls back all the changes to objects in the database associated with this transaction. If this transaction has been aborted or completed, then this method throws an error event.

IDBTransaction.objectStore

Returns an IDBObjectStore object representing an object store that is part of the scope of this transaction.

Mode constants

Transactions can have one of three modes:

Even if these constants are now deprecated, you can still use them to provide backward compatibility if required (in Chrome the change was made in version 21). You should code defensively in case the object is not available anymore:

var myIDBTransaction = window.IDBTransaction || window.webkitIDBTransaction || { READ_WRITE: "readwrite" };

Example

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. For a full working example, see our To-do Notifications app (view example live.)

// Let us open our database
var DBOpenRequest = window.indexedDB.open("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;
    
  // Add the data to the database
  addData();
};

function addData() {
  // Create a new object to insert 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 to add 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. Duplicate items not allowed.</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 the request (this does not mean the item
    // has been stored successfully in the DB - for that you need transaction.oncomplete)
    note.innerHTML += '<li>Request successful.</li>';
  };
};

Specifications

Browser compatibilityUpdate compatibility data on GitHub

See also

• Using IndexedDB
• Starting transactions: IDBDatabase
• Using transactions: IDBTransaction
• Setting a range of keys: IDBKeyRange
• Retrieving and making changes to your data: IDBObjectStore
• Using cursors: IDBCursor
• Reference example: To-do Notifications (view example live.)