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

The operation read-only property of the DataStoreTask interface returns the type of operation that represents the current change that has been made to the data store.

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


myOperation = task.operation;


A DataStoreOperation (see Operation types).


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.

In each case, task.operation is checked to see what type each task is, then appropriate action is taken.

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 record is added into the data store.
update The record is updated in the data store.
remove The record is deleted from the data store.
clear All the records are deleted from the data store. 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 'operation' 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 operation Property Reference Référence storage Storage