Dec 20, 2019
IndexedDB API
IndexedDB is a low-level API for client-side storage of significant amounts of structured data, including files/blobs. This API uses indexes to enable high-performance searches of this data. While Web 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.
Note: This feature is available in Web Workers.
Note: IndexedDB API is powerful, but may seem too complicated for simple cases. If you’d prefer a simple API, try libraries such as localForage, dexie.js, ZangoDB, PouchDB, idb, idb-keyval, JsStore and lovefield that make IndexedDB more programmer-friendly.
Key concepts and usage
IndexedDB is a transactional database system, like an SQL-based RDBMS. However, unlike SQL-based RDBMSes, which use fixed-column tables, 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.
- Combine IndexedDB for storing data offline with Service Workers for storing assets offline, as outlined in Making PWAs work offline with Service workers.
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
Operations performed using IndexedDB are done asynchronously, so as not to block applications. IndexedDB originally included both synchronous and asynchronous APIs. The synchronous API was intended for use only with Web Workers but was removed from the spec because it was unclear whether it was needed. However, the synchronous API may be reintroduced if there is enough demand from web developers.
Storage limits and eviction criteria
There are a number of web technologies that store data of one kind or another on the client-side (i.e. on your local disk). IndexedDB is most commonly talked about. The process by which the browser works out how much space to allocate to web data storage and what to delete when that limit is reached is not simple and differs between browsers. Browser storage limits and eviction criteria attempt to explain how this works, at least in the case of Firefox.
Interfaces
To get access to a database, call open() on the indexedDB the 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
IDBEnvironmentProvides access to IndexedDB functionality. It is implemented by the window and worker objects. This interface isn't part of the 2.0 specification.IDBFactoryIt provides access to a database. This is the interface implemented by the global object indexedDB and is, therefore, the entry point for the API.IDBOpenDBRequestRepresents a request to open a database.IDBDatabaseRepresents a connection to a database. It's the only way to get a transaction on the database.
Retrieving and modifying data
IDBTransactionRepresents 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.IDBRequestGeneric interface that handles database requests and provides access to results.IDBObjectStoreRepresents an object store that allows access to a set of data in an IndexedDB database, looked up via primary key.IDBIndexAlso 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.IDBCursorIterates over object stores and indexes.IDBCursorWithValueIterates over object stores and indexes and returns the cursor's current value.IDBKeyRangeDefines a key range that can be used to retrieve data from a database in a certain range.IDBLocaleAwareKeyRange Defines a key range that can be used to retrieve data from a database in a certain range, sorted according to the rules of the locale specified for a certain index (see createIndex()'s optionalParameters.). This interface isn't part of the 2.0 specification.
Custom event interfaces
This specification fires events with the following custom interface:
IDBVersionChangeEventThe IDBVersionChangeEvent interface indicates that the version of the database has changed, as the result of an IDBOpenDBRequest.onupgradeneeded event handler function.
Obsolete interfaces
An early version of the specification also defined the following, now removed, interfaces. They are still documented in case you need to update previously written code:
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.
Represents exception conditions that can be encountered while performing database operations.
Sync version of IDBTransaction.
IDBObjectStoreSync Sync version of IDBObjectStore.
IDBIndexSync Sync version of IDBIndex.
IDBFactorySync Sync version of IDBFactory.
IDBEnvironmentSync Sync version of IDBEnvironment.
IDBDatabaseSync Sync version of IDBDatabase.
IDBCursorSync Sync version of IDBCursor.
Read More About IndexedDB API
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