Docker-compose: node_modules not present in a volume after npm install succeeds

I have an app with the following services: web/ - holds and runs a python 3 flask web server on port 5000. Uses sqlite3. worker/ - has an index.js file which is a worker for a queue. the web server interacts with this queue using a json API over port 9730. The worker uses redis for storage. The worker also stores data locally in the folder worker/images/ Now this question only concerns the worker.