npm prune [[<@scope>/]<pkg>...] [--production]
This command removes "extraneous" packages. If a package name is provided, then only packages matching one of the supplied names are removed.
Extraneous packages are packages that are not listed on the parent package's dependencies list.
If the --production flag is specified or the NODE_ENV environment variable is set to production, this command will remove the packages specified in your devDependencies. Setting --production=false will negate NODE_ENV being set to production.