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.
There is a performance cost associated with looking at the value property of a cursor, because the object is created lazily. To use a feature like getAll(), Gecko would have to create all the objects at once. If you were just interested in looking at each of the keys, for instance, it would be much more efficient to use a cursor. If you were trying to get an array of all the objects in an object store, though, you could use getAll().
The locale read-only property of the IDBIndex interface returns the locale of the index (for example en-US, or pl) if it had a locale value specified upon its creation (see createIndex()'s optionalParameters.) Note that this property always returns the current locale being used in this index, in other words, it never returns "auto".