IDBObjectStore: createIndex() method
====================================

 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.

**Note:** This feature is available in Web Workers

Syntax
------


```js
createIndex(indexName, keyPath)
createIndex(indexName, keyPath, options)
```

### 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`.


`options` Optional

 An object which can include the following
 properties:


`unique`

If `true`, the index will not allow duplicate values for a single key. Defaults to `false`.

`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. Defaults to `false`.


`locale` 
Non-standard

 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:

`ConstraintError` `DOMException`

Thrown if an index with the same name already exists in the database. Index names are case-sensitive.

`InvalidAccessError` `DOMException`

Thrown if the provided key path is a sequence, and `multiEntry` is set to `true` in the `objectParameters` object.

`InvalidStateError` `DOMException`

Thrown if:

* The method was not called from a `versionchange` transaction mode callback, i.e. from inside a `onupgradeneeded` handler.
* The object store has been deleted.

`SyntaxError` `DOMException`

Thrown if the provided `keyPath` is not a valid key path.

`TransactionInactiveError` `DOMException`

 Thrown 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
 Firefox bug 1176165.)


Examples
--------

 In the following example you can see
 the `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).


```js
let db;

// Let us open our database
const DBOpenRequest = window.indexedDB.open("toDoList", 4);

// Two event handlers for opening the database.
DBOpenRequest.onerror = (event) => {
  note.innerHTML += "<li>Error loading database.</li>";
};

DBOpenRequest.onsuccess = (event) => {
  note.innerHTML += "<li>Database initialized.</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 = (event) => {
  const db = event.target.result;

  db.onerror = (event) => {
    note.innerHTML += "<li>Error loading database.</li>";
  };

  // Create an objectStore for this database
  const 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
--------------

| Specification |
| --- |
| Indexed Database API 3.0 # ref-for-dom-idbobjectstore-createindex① |

Browser compatibility
---------------------

BCD tables only load in the browser with JavaScript enabled. Enable JavaScript to view data.

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 the example live).