This API is available on Firefox OS for internal applications only.

The DataStoreTask interface of the Data Store API represents a record changed in the data store when a DataStoreCursor is used to iterate through the data store's change history.

Note: The Data Store API is available in Web Workers, from Firefox 32 onwards (Firefox OS 2.0; see bug 949325.)

Properties Read only
Returns the data stored in the changed record in the data store. Must return null if the operation is clear or done. Read only
Returns the identifier of the changed record in the data store. Must return null if the operation is clear or done.
DataStoreTask.operation Read only
Returns the type of operation that represents the current change that has been made to the data store.
DataStoreTask.revisionId Read only
Returns the id of the current revision of the data store, i.e. the current change that has been made to a data record.


In the following example, we use navigator.getDataStores to return a list of DataStore objects representing data stores on the device called contacts. Since there is only one such data store, we can access it inside the outer promise using stores[0]. The next promise uses DataStore.getLength to return the number of records in the store. If the value is 0, we populate the data store with records contained in the contactsInit object; if there is already data in the store, we run DataStore.sync to create a DataStoreCursor object allowing us to loop through any additions since the code last accessed the data store and update the data display as necessary.

The cursor is passed to the runNextTask() function, which calls to start the process of managing the next task — the resulting DataStoreTask object is passed to the manageTask() function to work out what to do with it. runNextTask() is then called repeatedly by manageTask() until the cursor has finished working through all the records.

navigator.getDataStores('contacts').then(function(stores) {
  stores[0].getLength().then(function(storeLength) {
    if(storeLength == 0) {
        for(i = 0; i < contactsInit.length; i++) {
    } else {
      var cursor = stores[0].sync();

function runNextTask(cursor) { {
   manageTask(cursor, task);

function manageTask(cursor, task) {
  if (task.operation == 'done') {
    // Finished adding contacts!

  if (task.operation == 'add') {
    // Add the contacts that are different to how it was before


Note: This code is taken from our Data Store Contacts Editor demo. Look through the code to help you understand better what is going on, and how the full code works.

Operation types

The different operation types used in DataStoreTask are (see also the spec definitions):

Enumeration Description
add The data record is added into the data store.
update The data record is updated in the data store.
remove The data record is deleted in the data store.
clear All the records are deleted from the data store; a clear operation (plus a list of add operations) is also received when the revision ID is too old for the DataStore to be able to provide all the steps to bring you to the current ID. The DataStore Service has a list of about 100 operations in memory.
done All changes are finished.

Note: These are currently different to the operation types returned by DataStoreChangeEvent. This discrepancy will be fixed soon at an appropriate time.


Specification Status Comment
Data Store API
The definition of 'DataStoreTask' in that specification.

The discussion concerning this API's creation happened in various Mozilla mailing lists and other places. A summary of the discussion and further pointers can be found on the Mozilla Wiki. For further feedback and questions, send mail to the dev-webapi mailing list.

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support No support No support No support No support No support
Feature Android Chrome Firefox Mobile (Gecko) Firefox OS IE Phone Opera Mobile Safari Mobile
Basic support No support No support No support 1.0.1 No support No support No support
Available in web workers No support No support No support 2.0 No support No support No support

See also


© 2016 Mozilla Contributors
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.

API Data Store Data Store API Database DataStoreTask Interface Non-standard Reference Référence storage Storage