I had node.js 0.12 before installing io.js 1.1.0, and was trying to figure out if npm now use iojs instead of node.

Currently npm --verbose will print following for io.js

npm info it worked if it ends with ok
npm verb cli [ 'node', '/usr/local/bin/npm', '--verbose' ]
npm info using npm@2.5.0
npm info using node@v1.1.0
npm verb node symlink /usr/local/bin/node

While from version number it's quite clear that npm is using io.js, if we expose runtime name in some fashion then npm can be improved with a clearer message.

ref: https://github.com/npm/npm/blob/master/bin/npm-cli.js#L58

(if there are existing ways, then i will open a PR on npm repo)