Short version: node.js of course!
A bit longer one:
One can fetch `jsverify` package metadata from http://registry.npmjs.org/jsverify and all current packages are listed in http://registry.npmjs.org/-/all (this one is special, its size is around 50MiB). Please cache your results, let's not DDoS the registry.
There are around one gigabyte of nice JSON data. After initial fetch you can traverse it using any tools you want. I naturally used node.js for that too.