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I am using ubuntu 11.10 and put npm bash completion under my .bashrc, works fine if do npm [tab] but, not for the package names. It just hangs and I have to Ctrl-C to take it out.
It will eventually return, it just takes a while.
$ npm install
Display all 8361 possibilities? (y or n)
On my system, it takes about 9 seconds from an empty cache. If your cache is full, it's much faster.
It'd be nice to rework that bit to respond more quickly somehow, but it's not exactly clear how to do that. It already caches quite agressively. It's fetching this page, which is quite large: http://registry.npmjs.org/-/short
In this case 9 seconds is good enough sir!