A setup for just fetching a package and unpacking.

fetch.js

var request = require('request');
var targz = require('tar.gz');
var semver = require('semver');
var JSONStream = require('JSONStream');
var concat = require('concat-stream');
var file = process.argv[2];
var dir = process.argv[3] || process.cwd();
function fetchUnpack(url, dir) {
  request(url).pipe(targz().createWriteStream(dir));
}
function fetchMetaData(name, cb) {
  request('https://registry.npmjs.org/' + name).pipe(JSONStream.parse()).pipe(concat(cb));
}
function getLatestVersion(d) {
  var pkg = d[0];
  var versions = pkg.versions;
  var greatest = '0.0.0';
  Object.keys(versions).forEach(function (v) {
    greatest = semver.gt(greatest, v) ? greatest : v;
  });
  return greatest;
}
function getTarballUrl(name, cb) {
  fetchMetaData(name, function (d) {
    cb(d[0].versions[getLatestVersion(d)].dist.tarball)
  });
}
getTarballUrl(file, function (url) {
  fetchUnpack(url, dir);
});

package.json

{
  "name": "fetch",
  "version": "1.0.0",
  "dependencies": {
    "request": "*",
    "JSONStream": "*",
    "tar.gz": "*",
    "semver": "*",
    "concat-stream": "*"
  }
}