From the Play 2.3 Migration Guide:
npm can be used as well as WebJars by declaring a package.json file in the root of your project. Assets from npm packages are extracted into the same lib folder as WebJars so that, from a code perspective, there is no concern whether the asset is sourced from a WebJar or from an npm package.
I can't find anything else about using npm in the newer docs. From the mentioned dependency com.typesafe.npm I can only find versions compiled with Scala 2.10:
Both won't work with Play 2.5. Are there newer versions compiled with Scala 2.11 or is npm not used / supported any more.