After some npm investigation I can claim that npm support covered in the issue description can be implemented pretty easily. However, in order to make the implementation generic I do believe that org.jboss.tools.jst.js plugin must be refactored. My proposal is to split it to:

• org.jboss.tools.jst.js.node (plugin with generic node tools launch, which will be subclassed for bower, npm etc. Node preferences + some utilities)
• org.jsboss.tools.jst.js.bower (bower specific stuff, will have org.jboss.tools.jst.js.node as required bundle )
  it will simplify the implementation of not only npm but also other node dependent tools (grunt, gulp etc.).