http://substack.net/task_automation_with_npm_run
sequential sub-tasks
If you have 2 tasks you want to run in series, you can just npm run each task separated by a &&:
"build": "npm run build-js && npm run build-css"
parallel sub-tasks
If you want to run some tasks in parallel, just use & as the separator!
"watch": "npm run watch-js & npm run watch-css"