IDBTransaction: mode property

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

Note: This feature is available in Web Workers.

The mode read-only property of the IDBTransaction interface returns the current mode for accessing the data in the object stores in the scope of the transaction (i.e., is the mode to be read-only, or do you want to write to the object stores?) The default value is readonly.

Value

An object defining the mode for isolating access to data in the current object stores: A string defining the mode for isolating access to data in the current object stores. The following values are available:

readonly

Allows data to be read but not changed.

readwrite

Allows reading and writing of data in existing data stores to be changed.

versionchange

Allows any operation, including ones that delete and create object stores and indexes. This mode is for updating the version number of transactions if the need is detected when calling IDBFactory.open(). Transactions of this mode cannot run concurrently with other transactions. Transactions in this mode are known as upgrade transactions.

Examples

In the following code snippet, we open a read/write transaction on our database and add some data to an object store. Note also the functions attached to transaction event handlers to report on the outcome of the transaction opening in the event of success or failure. At the end, we log the mode of the current transaction using mode. For a full working example, see our To-do Notifications app (view example live).

js
const note = document.getElementById("notifications");

// an instance of a db object for us to store the IDB data in
let db;

// Let us open our database
const DBOpenRequest = window.indexedDB.open("toDoList", 4);

DBOpenRequest.onsuccess = (event) => {
  note.appendChild(document.createElement("li")).textContent =
    "Database initialized.";

  // store the result of opening the database in the db variable.
  // This is used a lot below
  db = DBOpenRequest.result;

  // Run the addData() function to add the data to the database
  addData();
};

function addData() {
  // Create a new object ready for being inserted into the IDB
  const newItem = [
    {
      taskTitle: "Walk dog",
      hours: 19,
      minutes: 30,
      day: 24,
      month: "December",
      year: 2013,
      notified: "no",
    },
  ];

  // open a read/write db transaction, ready for adding the data
  const transaction = db.transaction(["toDoList"], "readwrite");

  // report on the success of opening the transaction
  transaction.oncomplete = (event) => {
    note.appendChild(document.createElement("li")).textContent =
      "Transaction completed: database modification finished.";
  };

  transaction.onerror = (event) => {
    note.appendChild(document.createElement("li")).textContent =
      "Transaction not opened due to error. Duplicate items not allowed.";
  };

  // create an object store on the transaction
  const objectStore = transaction.objectStore("toDoList");

  // add our newItem object to the object store
  const objectStoreRequest = objectStore.add(newItem[0]);

  objectStoreRequest.onsuccess = (event) => {
    // report the success of the request (this does not mean the item
    // has been stored successfully in the DB - for that you need transaction.onsuccess)
    note.appendChild(document.createElement("li")).textContent =
      "Request successful.";
  };

  // Return the mode this transaction has been opened in (should be "readwrite" in this case)
  transaction.mode;
}