**level-index-update** is a Node.js utility that wraps LevelDB to keep secondary indexes in sync with document updates. It generates a single batch of `put` and `del` operations that removes old index entries and inserts new ones based on a user‑provided mapper, and can also expand arbitrary write batches to include the necessary index updates. The library is aimed at developers building applications on LevelDB who need automatic, batch‑wise maintenance of mutable secondary indexes.