IndexedDB

Key concepts and usage

IndexedDB is a transactional database system, like a SQL-based RDBMS; however whereas the latter uses tables with fixed columns, IndexedDB is a JavaScript-based object-oriented database. IndexedDB lets you store and retrieve objects that are indexed with a key; any objects supported by the structured clone algorithm can be stored. You need to specify the database schema, open a connection to your database, and then retrieve and update data within a series of transactions.

• Read more about the Concepts behind IndexedDB
• Learn to use IndexedDB asynchronously from first principles with our Using IndexedDB guide
• Find developer recommendations for making web apps work offline at our Offline Apps page.

Synchronous and asynchronous

Operations performed using IndexedDB are done asynchronously, so as not to block the rest of an application's running. IndexedDB originally included both an asynchronous API and a synchronous API; the synchronous API being intended for use only with Web Workers. The synchronous version was removed from the spec because its need was questionable, however it may be reintroduced in the future if there is enough demand from web developers.

Storage limits

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

• Firefox has no limit on the IndexedDB database's size. The user interface will just ask permission for storing blobs bigger than 50 MB. This size quota can be customized through the dom.indexedDB.warningQuota preference (which is defined in http://mxr.mozilla.org/mozilla-central/source/modules/libpref/src/init/all.js).
• Google Chrome: see https://developers.google.com/chrome...rage#temporary.

IndexedDB Interfaces

To get 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 IndexedDB functionality. 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.

IDBRequest

Generic interface that handles database requests and provides access to results.

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 readwrite) that you want.

IDBObjectStore

Represents an object store that allows access to a set of data in an IndexedDB database, looked up via primary key.

IDBIndex

Also allows access to a subset of data in an IndexedDB database, but uses an index to retrieve the record(s) rather than the primary key. This is sometimes faster than using IDBObjectStore.

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 that can be used to retrieve data from a database in a certain range.

Custom event interfaces

This specification fires events with the following custom interface:

IDBVersionChangeEvent

The IDBVersionChangeEvent interface indicates that the version of the database has changed, as the result of an IDBOpenDBRequest.onupgradeneeded event handler function.

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.

Examples

• eLibri: A powerful library and eBook reader application, written by Marco Castelluccio, winner of the IndexedDB Mozilla DevDerby.
• To-do Notifications (view example live): The reference application for the examples in the reference docs.
• Storing images and files in IndexedDB
• IndexedDB Examples

Browser compatibility

Specifications

See also

• localForage: A Polyfill providing a simple name:value syntax for client-side data storage, which uses IndexedDB in the background, but falls back to WebSQL and then localStorage in browsers that don't support IndexedDB.
• dexie.js: A wrapper for IndexedDB that allows much faster code development via nice, simple syntax.