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• 句法
• 范例
• 规范
• 浏览器兼容性
• 另请参阅
• 相关话题

count() 方法在 IDBIndex interface returns an IDBRequest object, and in a separate thread, returns the number of records within a key range.

句法

var request = myIndex.count();
var request = myIndex.count(key);
					

参数

key 可选

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

返回值

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

异常

此方法可能引发 DOMException of one of the following types:

异常	描述
TransactionInactiveError	This IDBIndex 's transaction is inactive.
DataError	The key or key range provided contains an invalid key.
InvalidStateError	IDBIndex has been deleted or removed.

范例

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 使用 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 IDBIndex-example demo repo ( View the example live )。

function displayDataByIndex() {
  tableEntry.innerHTML = '';
  var transaction = db.transaction(['contactsList'], 'readonly');
  var objectStore = transaction.objectStore('contactsList');
  var myIndex = objectStore.index('lName');
  var countRequest = myIndex.count();
  countRequest.onsuccess = function() {
    console.log(countRequest.result);
  }
  myIndex.openCursor().onsuccess = function(event) {
    var cursor = event.target.result;
    if(cursor) {
      var 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.');
    }
  };
};
						

规范

规范	状态	注释
索引数据库 API 2.0 The definition of 'count()' in that specification.	推荐
索引数据库 API 草案 The definition of 'count()' in that specification.	推荐

浏览器兼容性

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request. 更新 GitHub 上的兼容性数据

	桌面						移动
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
count	Chrome 24 24 23 — 24 Prefixed Prefixed Implemented with the vendor prefix: webkit	Edge 12	Firefox 16 16 10 — 16 Prefixed Prefixed Implemented with the vendor prefix: moz	IE 部分支持 10	Opera 15	Safari 7	WebView Android Yes Yes ? — ? Prefixed Prefixed Implemented with the vendor prefix: webkit	Chrome Android 25	Firefox Android 22	Opera Android 14	Safari iOS 8	Samsung Internet Android 1.5

图例

完整支持

完整支持

部分支持

部分支持

要求使用供应商前缀或不同名称。

要求使用供应商前缀或不同名称。

另请参阅

• 使用 IndexedDB
• 开始事务： IDBDatabase
• 使用事务： IDBTransaction
• 设置一系列键： IDBKeyRange
• 检索并使您的数据改变： IDBObjectStore
• 使用光标： IDBCursor
• 参考范例： 待办通知 ( 实时查看范例 )。

元数据

• 最后修改： 2020 年 1 月 22 日

相关话题

1. IndexedDB API
2. IDBIndex
3. 特性

   1. isAutoLocale
   2. keyPath
   3. locale
   4. multiEntry
   5. 名称
   6. objectStore
   7. unique
4. 方法

   1. count()
   2. get()
   3. getAll()
   4. getAllKeys()
   5. getKey()
   6. openCursor()
   7. openKeyCursor()
5. IndexedDB 相关页面

   1. IDBCursor
   2. IDBCursorSync
   3. IDBCursorWithValue
   4. IDBDatabase
   5. IDBDatabaseException
   6. IDBDatabaseSync
   7. IDBEnvironment
   8. IDBEnvironmentSync
   9. IDBFactory
   10. IDBFactorySync
   11. IDBIndexSync
   12. IDBKeyRange
   13. IDBObjectStore
   14. IDBObjectStoreSync
   15. IDBOpenDBRequest
   16. IDBRequest
   17. IDBTransaction
   18. IDBTransactionSync
   19. IDBVersionChangeEvent
   20. IDBVersionChangeRequest