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    This article is in need of a technical review.

    The unique property returns a boolean that states whether the index allows duplicate keys or not.

    This is decided when the index is created, using the IDBObjectStore.createIndex method. This method takes an optional parameter, unique, which if set to true means that the index will not be able to accept duplicate entries.


    var myIndex = objectStore.index('index');


    A Boolean:

    Value Effect
    true The current index does not allow duplicate values for a key.
    false The current index allows duplicate key values.


    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 basic cursor on the index using IDBIndex.openCursor — this works the same as opening a cursor directly on an ObjectStore using IDBObjectStore.openCursor except that the returned records are sorted based on the index, not the primary key.

    The unique status of the index is logged to the console: it should be returned as false.

    Finally, we iterate through each record, and insert the data into an HTML table. For a complete working example, see our IDBIndex-example demo repo (View the example live.)

    function displayDataByIndex() {
      tableEntry.innerHTML = '';
      var transaction = db.transaction(['contactsList'], 'readonly');
      var objectStore = transaction.objectStore('contactsList');
      var myIndex = objectStore.index('lName'); 
      myIndex.openCursor().onsuccess = function(event) {
        var cursor =;
        if(cursor) {
          var tableRow = document.createElement('tr');
          tableRow.innerHTML =   '<td>' + + '</td>'
                               + '<td>' + cursor.value.lName + '</td>'
                               + '<td>' + cursor.value.fName + '</td>'
                               + '<td>' + cursor.value.jTitle + '</td>'
                               + '<td>' + + '</td>'
                               + '<td>' + cursor.value.eMail + '</td>'
                               + '<td>' + + '</td>'
                               + '<td>' + cursor.value.age + '</td>';
        } else {
          console.log('Entries all displayed.');    


    Specification Status Comment
    Indexed Database API
    The definition of 'unique' in that specification.
    Candidate Recommendation  

    Browser compatibility

    Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
    Basic support 23webkit
    10 moz
    16.0 (16.0)
    10, partial 15 7.1
    count() 23 22.0 (22.0) 10, partial 15 7.1
    getAll() and getAllKeys() Not supported 24.0 (24.0)
    behind dom.indexedDB.experimental  pref
    Not supported Not supported Not supported
    Feature Android Firefox Mobile (Gecko) Firefox OS IE Phone Opera Mobile Safari Mobile
    Basic support 4.4 22.0 (22.0) 1.0.1 10 22 Not supported
    count() 4.4 22.0 (22.0) 1.0.1 10 22 Not supported
    getAll() and getAllKeys() Not supported 24.0 (24.0)
    behind dom.indexedDB.experimental  pref
    1.1 behind
    dom.indexedDB.experimental  pref
    Not supported Not supported Not supported

    Be careful in Chrome as it still implements the old specification along the new one. Similarly it still has the prefixed webkitIndexedDB property even if the unprefixed indexedDB is present.

    See also

    Document Tags and Contributors

    Contributors to this page: fscholz, chrisdavidmills
    Last updated by: fscholz,