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 result property and an error event is fired (error).
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).
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 databasevar DBOpenRequest = window.indexedDB.open("toDoList",4);// these two event handlers act on the database being// opened successfully, or not
note.innerHTML +='<li>Error loading database.</li>';};
note.innerHTML +='<li>Database initialized.</li>';// store the result of opening the database.
db = DBOpenRequest.result;};