How do you prevent install of "devDependencies" NPM modules for Node.js (package.json)?

I have this in my package.json file (shortened version):

{
  "name": "a-module",
  "version": "0.0.1",
  "dependencies": {
    "coffee-script":      ">= 1.1.3"
  },
  "devDependencies": {
    "stylus":             ">= 0.17.0"
  }
}

I am using NPM version 1.1.1 on Mac 10.6.8.

When I run the following command from the project root, it installs both the dependencies and devDependencies:

npm install

I was under the impression that this command installed the devDependencies:

npm install --dev

How do I make it so npm install only installs dependencies (so production environment only gets those modules), while something like npm install --dev installs both dependencies and devDependencies?

The npm install command will install the devDependencies along other dependencies when run inside a package directory, in a development environment (the default).

In version 8.x and above use --omit=dev flag to install only regular dependencies:

npm install --omit=dev

This will install only dependencies, and not devDependencies, regardless of the value of the NODE_ENV environment variable.

If you use 6.x or an earlier version, you need to use the --only=prod flag instead.

Note:
Before v3.3.0 of npm (2015-08-13), the option was called --production, i.e.

npm install --production

You may also need --no-optional flag.