The createIndex() method of the IDBObjectStore interface creates and returns a new IDBIndex object in the connected database.

Note that this method must be called only from a VersionChange transaction mode callback.

Note: This feature is available in Web Workers.


objectStore.createIndex(objectIndexName, objectKeypath, optionalObjectParameters);


An IDBIndex object: the newly created index.


The name of the index to create. Note that it is possible to create an index with an empty name.
The key path for the index to use. Note that it is possible to create an index with an empty keyPath, and also to pass in an array as a keyPath.

The IDBIndexParameters object — whose attributes are optional parameters to the method — can include the following properties:

Attribute Description
unique If true, the index will not allow duplicate values for a single key.
multiEntry If true, the index will add an entry in the index for each array element when the keyPath resolves to an Array. If false, it will add one single entry containing the Array.

Currently Firefox-only (43+), this allows you to specify a locale for the index. Any sorting operations performed on the data via key ranges will then obey sorting rules of that locale (see locale-aware sorting.) You can specify its value in one of three ways:

  • string: A string containing a specific locale code, e.g. en-US, or pl.
  • auto: The platform default locale will be used (may be changed by user agent settings.)
  • null or undefined: If no locale is specified, normal JavaScript sorting will be used — not locale-aware.


This method may raise a DOMException of one of the following types:

Exception Description
InvalidStateError Occurs if the method was not called from a versionchange transaction mode callback.
TransactionInactiveError Occurs if the transaction this IDBObjectStore belongs to is not active (e.g. has been deleted or removed.) In Firefox previous to version 41, an InvalidStateError was raised in this case as well, which was misleading; this has now been fixed (see bug 1176165.)
ConstraintError Occurs if an index with the same name (case-sensitive) already exists in the database.


In the following example you can see the IDBOpenDBRequest.onupgradeneeded handler being used to update the database structure if a database with a higher version number is loaded. createIndex() is used to create new indexes on the object store.  For a full working example, see our To-do Notifications app (view example live.)

var db;

// Let us open our database
var DBOpenRequest ="toDoList", 4);

// these two event handlers act on the database being opened successfully, or not
DBOpenRequest.onerror = function(event) {
  note.innerHTML += '<li>Error loading database.</li>';

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 = request.result;
  // Run the displayData() function to populate the task list with all the to-do list data already in the IDB

// This event handles the event whereby a new version of the database needs to be created
// Either one has not been created before, or a new version number has been submitted via the
// line above
//it is only implemented in recent browsers
DBOpenRequest.onupgradeneeded = function(event) {
  var db =;
  db.onerror = function(event) {
    note.innerHTML += '<li>Error loading database.</li>';

  // Create an objectStore for this database   
  var objectStore = db.createObjectStore("toDoList", { keyPath: "taskTitle" });

  // define what data items the objectStore will contain
  objectStore.createIndex("hours", "hours", { unique: false });
  objectStore.createIndex("minutes", "minutes", { unique: false });
  objectStore.createIndex("day", "day", { unique: false });
  objectStore.createIndex("month", "month", { unique: false });
  objectStore.createIndex("year", "year", { unique: false });
  objectStore.createIndex("notified", "notified", { unique: false });


Specification Status Comment
Indexed Database API
The definition of 'createIndex()' in that specification.
Editor's Draft  

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support 23webkit
10 moz
16.0 (16.0)
10, partial 15 7.1
Available in workers (Yes) 37.0 (37.0) ? (Yes) ?
Feature Android Firefox Mobile (Gecko) Firefox OS IE Phone Opera Mobile Safari Mobile
Basic support 4.4 22.0 (22.0) 1.0.1 10 22 8
Available in workers (Yes) 37.0 (37.0) (Yes) ? (Yes) ?

See also




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

API createIndex Database IDBObjectStore IndexedDB Method Reference storage Storage