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

The data read-only property of the DataStoreChangeEvent interface returns the data stored in the changed record in the data store. Must return null if the operation is clear or done.

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


myId =;


Any (whatever data type the object contained in the data record has.)


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.

When an add operation is found, the displayExisting() function is passed the and to be used in displaying the record in the app UI.

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.


Specification Status Comment
Data Store API
The definition of 'data' 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

Document Tags and Contributors

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