IndexedDB

IndexedDB is an API for client-side storage of significant amounts of structured data and for high performance searches on this data using indexes. While DOM Storage is useful for storing smaller amounts of data, it is less useful for storing larger amounts of structured data. IndexedDB provides a solution. This is the main landing page for MDN's IndexedDB coverage — here we provide links to the full API reference and usage guides, browser support details, and some explanation of key concepts.

Key concepts and usage

IndexedDB is a transactional database system, which is initially confusing if you are only used to working with relational databases, but becomes clear soon enough. IndexedDB lets you store and retrieve objects that are indexed with a key. You need to specify the database schema, open a connection to your database, and then retrieve and update data within a series of transactions.

Note: Like most web storage solutions, IndexedDB follows a same-origin policy. So while you can access stored data within a domain, you cannot access data across different domains.

Synchronous and asynchronous

IndexedDB includes both an asynchronous API and a synchronous API. The asynchronous API can be used in most cases, including WebWorkers, while the synchronous API is intended for use only with Web Workers and will be used more rarely.

Note: Currently, no major browser supports the synchronous API.

Storage limits

There isn't any limit on a single database item's size, however there may be a limit on each IndexedDB database's total size. This limit (and the way the user interface will assert it) may vary from one browser to another:

Asynchronous API

The asynchronous API methods return without blocking the calling thread. To get asynchronous access to a database, call open() on the indexedDB attribute of a window object. This method returns an IDBRequest object; asynchronous operations communicate to the calling application by firing events on IDBRequest objects.

Connecting to a database

IDBEnvironment
Provides access to a client-side database. It is implemented by the window and worker objects.
IDBFactory
Provides access to a database. This is the interface implemented by the global object indexedDB and is therefore the entry point for the API.
IDBOpenDBRequest
Represents a request to open a database.
IDBDatabase
Represents a connection to a database. It's the only way to get a transaction on the database.

Accessing results of database requests

IDBRequest
Provides access to results of asynchronous requests to databases and database objects. It is what you get when you call an asynchronous method.

Retrieving and modifying data

IDBTransaction
Represents a transaction. You create a transaction on a database, specify the scope (such as which object stores you want to access), and determine the kind of access (read only or write) that you want.
IDBObjectStore
Represents an object store.
IDBIndex
Provides access to the metadata of an index.
IDBCursor
Iterates over object stores and indexes.
IDBCursorWithValue
Iterates over object stores and indexes and returns the cursor's current value.
IDBKeyRange
Defines a range of keys.

Deprecated interfaces

An early version of the specification also defined these now removed interfaces. They are still documented in case you need to update previously written code:

IDBVersionChangeRequest
Represents a request to change the version of a database. The way to change the version of the database has since changed (by calling IDBFactory.open without also calling IDBDatabase.setVersion), and the interface IDBOpenDBRequest now has the functionality of the removed IDBVersionChangeRequest.
IDBDatabaseException 
Represents exception conditions that can be encountered while performing database operations.

Synchronous API

Important: This is a reminder that the synchronous version of IndexedDB is not yet implemented in any browser.

To get synchronous access to a database, call open() on the Unimplemented indexedDBSync attribute of a worker object. This returns an IDBDatabaseSync object, which enables you to create, open, and remove object stores and indexes, set the version of the database, and create transactions.

Examples

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Asynchronous API

11.0 webkit
24

4.0 (2.0) moz
16.0 (16.0)
10 17 Not supported
Synchronous API
(used with WebWorkers)
Not supported Not supported
See bug 701634
Not supported Not supported Not supported
Feature Android Firefox Mobile (Gecko) IE Phone Opera Mobile Safari Mobile
Asynchronous API 4.4 6.0 (6.0) moz
16.0 (16.0)
10 17 Not supported

Note: Some browsers don't yet support IndexedDB but do support WebSQL, most notably Safari/Webkit on desktop and iOS. One way around this problem is to use an IndexedDB Polyfill or Shim that falls back to WebSQL or even localStorage for non-supporting browsers. The best available polyfill at present is localForage.

Specifications

Specification Status Comment
Indexed Database API Candidate Recommendation