IDBObjectStore.createIndex()

The createIndex() method of the IDBObjectStore interface creates and returns a new IDBIndex object in the connected database. It creates a new field/column defining a new data point for each database record to contain.

Bear in mind that IndexedDB indexes can contain any JavaScript data type; IndexedDB uses the structured clone algorithm to serialize stored objects, which allows for storage of simple and complex objects.

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

Syntax

var myIDBIndex = objectStore.createIndex(indexName, keyPath);
var myIDBIndex = objectStore.createIndex(indexName, keyPath, objectParameters);

Parameters

indexName

The name of the index to create. Note that it is possible to create an index with an empty name.

keyPath

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 a sequence (array) as a keyPath.

objectParameters Optional

An IDBIndexParameters object, which 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.
locale	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.

Return value

An IDBIndex object: the newly created index.

Exceptions

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

Example

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 = window.indexedDB.open("toDoList", 4);

// Two event handlers for opening the database.
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
  displayData();
};

// This handler fires when a new database is created and indicates
// either that one has not been created before, or a new version
// was submitted with window.indexedDB.open(). (See above.)
// It is only implemented in recent browsers.
DBOpenRequest.onupgradeneeded = function(event) {
  var db = event.target.result;

  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 });
};

Specifications

Browser compatibility

See also

• Using IndexedDB
• Starting transactions: IDBDatabase
• Using transactions: IDBTransaction
• Setting a range of keys: IDBKeyRange
• Retrieving and making changes to your data: IDBObjectStore
• Using cursors: IDBCursor
• Reference example: To-do Notifications (view example live.)