Best practices

You can speed up data access by using the right scope and mode in the transaction. Here's a couple of tips:

• When defining the scope, specify only the object stores you need. This way, you can run multiple transactions with non-overlapping scopes concurrently.
• Only specify a READ_WRITE transaction mode when necessary. You can concurrently run multiple READ_ONLY transactions with overlapping scopes, but you can have only one READ_WRITE transaction for an object store. To learn more, see the definition for transactions in the Basic Concepts article. 

Example

In the following code snippet, we open a transaction and add data to the object store.  Because the specification is still evolving, Chrome uses prefixes in the methods. Chrome uses the webkit prefix. For example, instead of just IDBTransaction.READ_WRITE, use webkitIDBTransaction.READ_WRITE. Firefox does not use prefixes, except in the opening method (mozIndexedDB). Event handlers are registered for responding to various situations.

// Take care of the browser prefixes.
if (window.indexedDb) {
} else if (window.webkitIndexedDB) {
    window.indexedDB = window.webkitIndexedDB;
    window.IDBTransaction = window.webkitIDBTransaction;
} else if (window.mozIndexedDB) {
    window.indexedDB = window.mozIndexedDB;
} else {
   /* Browser not supported. */
}
   
...   

var idbReq = window.indexedDB.open('Database Name');
idbReq.onsuccess = function(event) {
   var db = this.result;
   var trans = db.transaction(['monster_store','hero_store'], IDBTransaction.READ_WRITE);
   var store = trans.objectStore('monster_store');
   var req = store.put(value, key);
   req.onsuccess = ...
   req.onerror = ...
};
idbReq.onerror = function(event) {
    ...
};

Mode constants

Transactions can have one of three modes:

abort()

Returns immediately, and undoes all the changes to objects in the database associated with this transaction. If this transaction has been aborted or completed, then this method throws an error event, with its code set to ABORT_ERR and a suitable message.

void abort(
);

All pending IDBRequest objects created during this transaction have their errorCode set to ABORT_ERR.

objectStore()

Returns an object store that has already been added to the scope of this transaction. Every call to this method on the same transaction object, with the same name, returns the same IDBObjectStore instance. If this method is called on a different transaction object, a different IDBObjectStore instance is returned.

IDBObjectStore objectStore(
  in DOMString name
) raises (IDBDatabaseException);