Sometimes when indexing, it is necessary to associate each document with certain additional metadata, for example, a set of tags, a number in the library catalog, the subject of a document, etc. To accomplish this task, additional fields can be added to each indexed document in addition to those already in the document itself.
Additional fields are associated with the document through the arguments of the FileIndexing event that occurs before indexing each added document....Search for Node.js / Developer Guide / Advanced...