Reflecting code changes in docker containers
Check out the section on Sharing Volumes. You should be able to share your host volume with the docker container and then any time you need a change you can just restart the server (or have something restart it for you!).
Your command would look something like: sudo docker run -v /src/webapp:/webapp --name test-container -d -p 80:3000 docker-express
Which mounts /src/webapp (on the host) to /webapp (in the container).