IDBRequest
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 (success
). If an error occurs while performing the operation, the exception is made available through the error
property and an error event is fired (error
).
The interface IDBOpenDBRequest
is derived from IDBRequest
.
Note: This feature is available in Web Workers
Instance 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 is not completed, the result is not available and an
InvalidStateError
exception is thrown. IDBRequest.source
Read only-
The source of the request, such as an
IDBIndex
or anIDBObjectStore
. If no source exists (such as when callingIDBFactory.open
), it returns null. IDBRequest.readyState
Read only-
The state of the request. Every request starts in the
pending
state. The state changes todone
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).
Instance methods
No methods, but inherits methods from EventTarget
.
Events
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.)
js
let db;
// Let us open our database
const DBOpenRequest = window.indexedDB.open("toDoList", 4);
// these two event handlers act on the database being
// opened successfully, or not
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.
db = DBOpenRequest.result;
};
Specifications
Specification |
---|
Indexed Database API 3.0 # request-api |
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 the example live).