Available on HTML5
IDBIndex interface of the IndexedDB API provides asynchronous access to an index in a database. An index is a kind of object store for looking up records in another object store, called the referenced object store. You use this interface to retrieve data.
Affects how the index behaves when the result of evaluating the index's key path yields an array. If
true, there is one record in the index for each item in an array of keys. If
false, then there is one record for each key that is an array.