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

The operation read-only property of the DataStoreChangeEvent 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 = e.operation;


A DataStoreOperation (see Operation types).


In the following snippet we retrieve all the data stores on the device with the name "contacts", then we use DataStore.sync to create a cursor to use for syncing the app with the current "content" data store (displaying new items, etc.) This cursor is passed to the runNextTask() function that will deal with running through the updates in some way. Next, we include some code inside an onchange function so that when a change is made we return the DataStoreChangeEvent (e in this case), find out what type of operation the change is, and then take action based on this type (either adding or deleting a contact's information.)

e.operation is used to check what type of operation the current change is.

navigator.getDataStores('contacts').then(function(stores) {
  var cursor = stores[0].sync();

  stores[0].onchange = function(e) {
    if (e.operation == 'removed') {
      // Delete the contact

    if (e.operation == 'added') {
      stores[0].get(e.id).then(function(obj) {
        // Add the new contact

Note: To see this code used in the context of a complete app, check out our The Data Store Contacts Viewer example changeevent version on GitHub.

Operation types

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

Enumeration Description
added The record is added into the data store.
updated The record is updated in the data store.
removed The record is deleted from the data store.
cleared All records are deleted from the data store.

Note: These are currently different to the operation types returned by DataStoreTask. 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

Supported in Firefox OS 1.0.1.
Available in web workers in Firefox OS 2.0.

See also

Document Tags and Contributors

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