Files on disk are the original database.
NodeJS is good at files.
path libraries have some slick and efficient ways of reading and writing files.
Remember that most of Node's I/O functions are asynchronous, so you may need to use callbacks, Promises, and/or async-await.
Heroku's Ephemeral Filesystem
you can write files to the
they will stay there for a while, but will disappear when your server restarts
...so for apps on Heroku at least, we need a better solution for storing data long-term