Retriever
A retriever in LlamaIndex is what is used to fetch Nodes from an index using a query string. For example, a ListIndexRetriever will fetch all nodes no matter the query. Meanwhile, a VectorIndexRetriever will only fetch the top-k most similar nodes.
const retriever = vector_index.asRetriever()
retriever.similarityTopK = 3;
// Fetch nodes!
const nodesWithScore = await retriever.retrieve("query string");