IDBIndex: count() method
========================

 The **`count()`** method of the `IDBIndex`
 interface returns an `IDBRequest` object, and in a separate thread,
 returns the number of records within a key range.

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

Syntax
------


```js
count()
count(key)
```

### Parameters

`key` Optional

The key or key range that identifies the record to be counted.

### Return value

A `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 the number of records that match the given key or key range.

### Exceptions

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

`TransactionInactiveError` `DOMException`

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

`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 basic cursor on
 the index using `IDBIndex.openCursor` — this works the same as opening a
 cursor directly on an `ObjectStore` using
 `IDBObjectStore.openCursor` except that the returned records are sorted
 based on the index, not the primary key.

`myIndex.count()` is then used to count the number of records in the index,
 and the result of that request is logged to the console when its success callback
 returns.

 Finally, we iterate through each record, and insert the data into an HTML table. For a
 complete working example, see our IndexedDB-examples demo repo (View the example live).


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

  const myIndex = objectStore.index("lName");
  const countRequest = myIndex.count();
  countRequest.onsuccess = () => {
    console.log(countRequest.result);
  };

  myIndex.openCursor().onsuccess = (event) => {
    const cursor = event.target.result;
    if (cursor) {
      const tableRow = document.createElement("tr");
      tableRow.innerHTML =
        `<td>${cursor.value.id}</td>` +
        `<td>${cursor.value.lName}</td>` +
        `<td>${cursor.value.fName}</td>` +
        `<td>${cursor.value.jTitle}</td>` +
        `<td>${cursor.value.company}</td>` +
        `<td>${cursor.value.eMail}</td>` +
        `<td>${cursor.value.phone}</td>` +
        `<td>${cursor.value.age}</td>`;
      tableEntry.appendChild(tableRow);

      cursor.continue();
    } else {
      console.log("Entries all displayed.");
    }
  };
}
```

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

| Specification |
| --- |
| Indexed Database API 3.0 # ref-for-dom-idbindex-count① |

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).