IDBIndex: openKeyCursor() method

The openKeyCursor() method of the IDBIndex interface returns an IDBRequest object, and, in a separate thread, creates a cursor over the specified key range, as arranged by this index.

The method sets the position of the cursor to the appropriate key, based on the specified direction.

If the key range is not specified or is null, then the range includes all the keys.

Note: Cursors returned by openKeyCursor() do not make the referenced value available as IDBIndex.openCursor does. This makes obtaining a list of keys much more efficient.

Note: This feature is available in Web Workers

Syntax

js

openKeyCursor()
openKeyCursor(range)
openKeyCursor(range, direction)

Parameters

range Optional

A key or IDBKeyRange to use as the cursor's range. If nothing is passed, this will default to a key range that selects all the records in this object store.

direction Optional

The cursor's direction. See IDBCursor Constants for possible values.

Return value

An IDBRequest object on which subsequent events related to this operation are fired.

If the operation is successful, the value of the request's result property is:

  • an IDBCursor object pointing at the first record matching the given query
  • null if no matching records were found.

Exceptions

This method may raise a DOMException of one of the following types:

TransactionInactiveError DOMException

Thrown if this IDBIndex's transaction is inactive.

TypeError

Thrown if the value for the direction parameter is invalid.

DataError DOMException

Thrown if the key or key range provided contains an invalid key.

InvalidStateError DOMException

Thrown if the IDBIndex has been deleted or removed.

Examples

In the following example we open a transaction and an object store, then get the index lName from a simple contacts database. We then open a key cursor on the index using openKeyCursor() — this works the same as opening a cursor directly on an ObjectStore using IDBObjectStore.openKeyCursor except that the returned records are sorted based on the index, not the primary key.

Finally, we iterate through each record in the index, and insert the last name and the corresponding primary key of the referenced record into an HTML table.

js

function displayDataByIndex() {
  tableEntry.innerHTML = "";
  const transaction = db.transaction(["contactsList"], "readonly");
  const objectStore = transaction.objectStore("contactsList");

  const myIndex = objectStore.index("lName");

  myIndex.openKeyCursor().onsuccess = (event) => {
    const cursor = event.target.result;
    if (cursor) {
      const tableRow = document.createElement("tr");
      tableRow.innerHTML =
        `<td>${cursor.key}</td>` + `<td>${cursor.primaryKey}</td>`;
      tableEntry.appendChild(tableRow);

      cursor.continue();
    } else {
      console.log("All last names displayed.");
    }
  };
}

Specifications

Specification
Indexed Database API 3.0
# ref-for-dom-idbindex-openkeycursor①

Browser compatibility

BCD tables only load in the browser

See also