node_modules/npm/lib/config/load-prefix.js

module.exports = loadPrefix

var findPrefix = require("./find-prefix.js")
var path = require("path")

function loadPrefix (cb) {
  var cli = this.list[0]

  Object.defineProperty(this, "prefix",
    { set : function (prefix) {
        var g = this.get("global")
        this[g ? "globalPrefix" : "localPrefix"] = prefix
      }.bind(this)
    , get : function () {
        var g = this.get("global")
        return g ? this.globalPrefix : this.localPrefix
      }.bind(this)
    , enumerable : true
    })

  Object.defineProperty(this, "globalPrefix",
    { set : function (prefix) {
        this.set("prefix", prefix)
      }.bind(this)
    , get : function () {
        return path.resolve(this.get("prefix"))
      }.bind(this)
    , enumerable : true
    })

  var p
  Object.defineProperty(this, "localPrefix",
    { set : function (prefix) { p = prefix },
      get : function () { return p }
    , enumerable: true })

  // try to guess at a good node_modules location.
  // If we are *explicitly* given a prefix on the cli, then
  // always use that.  otherwise, infer local prefix from cwd.
  if (Object.prototype.hasOwnProperty.call(cli, "prefix")) {
    p = path.resolve(cli.prefix)
    process.nextTick(cb)
  } else {
    findPrefix(process.cwd(), function (er, found) {
      p = found
      cb(er)
    })
  }
}