Docker is telling you that the command hit an error.
It is trying to run the node image with the command -w.
Since -w is not a command, it throws this error.
This is because you have written node in a place you probably didn’t mean to.
Your command is being interpreted like this:
docker run -p [port_info] -v [volume_info] node [command]
You can rewrite your command like so and it should work fine:
docker run -p 8085:3000 -v /home/joel/workspace/plural_docker_webdev:/var/www -w "/var/www" node npm start