IDBRequest - Web APIs 编辑

The IDBRequest interface of the IndexedDB API provides access to results of asynchronous requests to databases and database objects using event handler attributes. Each reading and writing operation on a database is done using a request.

The request object does not initially contain any information about the result of the operation, but once information becomes available, an event is fired on the request, and the information becomes available through the properties of the IDBRequest instance.

All asynchronous operations immediately return an IDBRequest instance. Each request has a readyState that is set to the 'pending' state; this changes to 'done' when the request is completed or fails. When the state is set to done, every request returns a result and an error, and an event is fired on the request. When the state is still pending, any attempt to access the result or error raises an InvalidStateError exception.

In plain words, all asynchronous methods return a request object. If the request has been completed successfully, the result is made available through the result property and an event indicating success is fired at the request (IDBRequest.onsuccess). If an error occurs while performing the operation, the exception is made available through the result property and an error event is fired (IDBRequest.onerror).

The interface IDBOpenDBRequest is derived from IDBRequest.

Note:

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Properties

Also inherits properties from EventTarget.

IDBRequest.error Read only

Returns a DOMException in the event of an unsuccessful request, indicating what went wrong.

IDBRequest.result Read only

Returns the result of the request. If the request failed and the result is not available, an InvalidStateError exception is thrown.

IDBRequest.source Read only

The source of the request, such as an IDBIndex or an IDBObjectStore. If no source exists (such as when calling IDBFactory.open), it returns null.

IDBRequest.readyState Read only

The state of the request. Every request starts in the pending state. The state changes to done when the request completes successfully or when an error occurs.

IDBRequest.transaction Read only

The transaction for the request. This property can be null for certain requests, for example those returned from IDBFactory.open unless an upgrade is needed. (You're just connecting to a database, so there is no transaction to return).

Methods

No methods, but inherits methods from EventTarget.

Events

Listen to these events using addEventListener() or by assigning an event listener to the oneventname property of this interface.

error

Fired when an error caused a request to fail.
Also available via the onerror property.

success

Fired when an IDBRequest succeeds.
Also available via the onsuccess property.

Example

In the following code snippet, we open a database asynchronously and make a request; onerror and onsuccess functions are included to handle the success and error cases. 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);

// these two event handlers act on the database being
// opened successfully, or not
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.
  db = DBOpenRequest.result;
};

Specifications

Browser compatibility

BCD tables only load in the browser

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.)