node/deps/npm/lib/prune.js

// prune extraneous packages.

module.exports = prune

prune.usage = 'npm prune [[<@scope>/]<pkg>...] [--production]'

var readInstalled = require('read-installed')
var npm = require('./npm.js')
var path = require('path')
var readJson = require('read-package-json')
var log = require('npmlog')

prune.completion = require('./utils/completion/installed-deep.js')

function prune (args, cb) {
  // check if is a valid package.json file
  var jsonFile = path.resolve(npm.dir, '..', 'package.json')
  readJson(jsonFile, log.warn, function (er) {
    if (er) return cb(er)
    next()
  })

  function next () {
    var opt = {
      depth: npm.config.get('depth'),
      dev: !npm.config.get('production') || npm.config.get('dev')
    }
    readInstalled(npm.prefix, opt, function (er, data) {
      if (er) return cb(er)
      prune_(args, data, cb)
    })
  }
}

function prune_ (args, data, cb) {
  npm.commands.unbuild(prunables(args, data, []), cb)
}

function prunables (args, data, seen) {
  var deps = data.dependencies || {}
  return Object.keys(deps).map(function (d) {
    if (typeof deps[d] !== 'object' || seen.indexOf(deps[d]) !== -1) return null
    seen.push(deps[d])
    if (deps[d].extraneous && (args.length === 0 || args.indexOf(d) !== -1)) {
      var extra = deps[d]
      delete deps[d]
      return extra.path
    }
    return prunables(args, deps[d], seen)
  }).filter(function (d) { return d !== null })
  .reduce(function FLAT (l, r) {
    return l.concat(Array.isArray(r) ? r.reduce(FLAT, []) : r)
  }, [])
}