IDBIndex: openKeyCursor() method
================================

 The **`openKeyCursor()`** method of the
 `IDBIndex` interface returns an `IDBRequest` object, and, in
 a separate thread, creates a cursor over the specified key range, as arranged by this
 index.

 The method sets the position of the cursor to the appropriate key, based on the
 specified direction.

If the key range is not specified or is null, then the range includes all the keys.

**Note:** Cursors returned by `openKeyCursor()` do not
 make the referenced value available as `IDBIndex.openCursor` does.
 This makes obtaining a list of keys much more efficient.


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

Syntax
------


```js
openKeyCursor()
openKeyCursor(range)
openKeyCursor(range, direction)
```

### Parameters

`range` Optional

 A key or `IDBKeyRange` to use as the cursor's range. If nothing is
 passed, this will default to a key range that selects all the records in this object
 store.


`direction` Optional

 The cursor's direction. See IDBCursor Constants for possible
 values.


### Return value

An `IDBRequest` object on which subsequent events related to this operation are fired.

If the operation is successful, the value of the request's `result` property is:

* an `IDBCursor` object pointing at the first record matching the given query
* `null` if no matching records were found.
### Exceptions

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

`TransactionInactiveError` `DOMException`

Thrown if this `IDBIndex`'s transaction is inactive.

`TypeError`

Thrown if the value for the direction parameter is invalid.

`DataError` `DOMException`

Thrown if the key or key range provided contains an invalid key.

`InvalidStateError` `DOMException`

Thrown if the `IDBIndex` has been deleted or removed.

Examples
--------

 In the following example we open a transaction and an object store, then get the
 index `lName` from a simple contacts database. We then open a key cursor on
 the index using `openKeyCursor()` — this works the same as opening a cursor
 directly on an `ObjectStore` using
 `IDBObjectStore.openKeyCursor` except that the returned records are sorted
 based on the index, not the primary key.

 Finally, we iterate through each record in the index, and insert the last name and the
 corresponding primary key of the referenced record into an HTML table.


```js
function displayDataByIndex() {
  tableEntry.innerHTML = "";
  const transaction = db.transaction(["contactsList"], "readonly");
  const objectStore = transaction.objectStore("contactsList");

  const myIndex = objectStore.index("lName");

  myIndex.openKeyCursor().onsuccess = (event) => {
    const cursor = event.target.result;
    if (cursor) {
      const tableRow = document.createElement("tr");
      tableRow.innerHTML =
        `<td>${cursor.key}</td>` + `<td>${cursor.primaryKey}</td>`;
      tableEntry.appendChild(tableRow);

      cursor.continue();
    } else {
      console.log("All last names displayed.");
    }
  };
}
```

Specifications
--------------

| Specification |
| --- |
| Indexed Database API 3.0 # ref-for-dom-idbindex-openkeycursor① |

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).