node.js sqlite transaction isolation

How do I ensure that SQLite doesn't interleave queries from multiple concurrent node.js/Express HTTP requests into a single transaction?

I would want DB queries from different requests to be executed in separate transactions, isolated from each other, allowing each to be committed or rolled back independently of each other. Given node.js's single-thread (and single-DB-connection?) characteristics this seems particularly problematic.

I've been trawling through dozens of web pages and docs and haven't found any clear (to me) explanation of how (or whether) this scenario is handled. For instance the description of db.serialize() only states that one query will be executed at a time - it says nothing about the separation of queries belonging to different transactions.

Any pointers appreciated!