IDBCursor.direction - Web APIs 编辑

The direction read-only property of the IDBCursor interface is a DOMString that returns the direction of traversal of the cursor (set using IDBObjectStore.openCursor for example). See the Values section below for possible values.

Note:

Syntax

var direction = cursor.direction;

Value

A string (defined by the IDBCursorDirection enum) indicating the direction in which the cursor is traversing the data. Possible values are:

Example

In this simple fragment we create a transaction, retrieve an object store, then use a cursor to iterate through all the records in the object store. Within each iteration we log the direction of the cursor, something like this:

prev

Note: we can't change the direction of travel of the cursor using the direction property, as it is read-only. We specify the direction of travel using the 2nd argument of IDBObjectStore.openCursor.

The cursor does not require us to select the data based on a key; we can just grab all of it. Also note that in each iteration of the loop, you can grab data from the current record under the cursor object using cursor.value.foo. For a complete working example, see our IDBCursor example (view example live.)

function backwards() {
  list.textContent = '';
  const transaction = db.transaction(['rushAlbumList'], 'readonly');
  const objectStore = transaction.objectStore('rushAlbumList');

  objectStore.openCursor(null,'prev').onsuccess = function(event) {
    const cursor = event.target.result;
      if(cursor) {
        const listItem = document.createElement('li');
        listItem.innerHTML = '<strong>' + cursor.value.albumTitle + '</strong>, ' + cursor.value.year;
        list.appendChild(listItem);

        console.log(cursor.direction);
        cursor.continue();
      } else {
        console.log('Entries displayed backwards.');
      }
  };
};

Specifications

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 example live.)