I just tried a basic install myself, here are the versions of npm and node I'm using as well:
13:01:05 pmuellr ~/tmp
$ npm install -g weinre
/usr/local/bin/weinre -> /usr/local/lib/node_modules/weinre/weinre
wei...@2.0.0-pre-I0Z7U9OV /usr/local/lib/node_modules/weinre
├── under...@1.7.0
├── no...@3.0.3 (abb...@1.0.7)
└── exp...@2.5.11 (q...@0.4.2, mi...@1.2.4, mkd...@0.3.0, con...@1.9.2)
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13:01:15 pmuellr ~/tmp
$ npm -v
2.10.1
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13:01:21 pmuellr ~/tmp
$ node -v
v2.1.0