"git clone" - purely in javascript

git-clone.js

/* eslint no-console:0 */

var git = require('git-node');
var fs = require('fs');
var pathJoin = require('path').join;

exports.clone = function clone(url, ref, target, cb) {
  var remote = git.remote(url);
  var repo = git.repo(pathJoin(target, 'git'));
  var opts = {onProgress: console.log};

  repo.fetch(remote, opts, function (err) {
    if (err) return cb(err);

    var read;

    repo.treeWalk(ref, function (err, stream) {
      if (err) return cb(err);
      read = stream.read;
      return read(onEntry);
    });

    function onEntry(err, entry) {
      if (err) return cb(err);
      if (!entry) return cb();

      var path = pathJoin(target, 'app', entry.path);
      console.log('%s %s', entry.hash, path);

      if (entry.type === 'tree') {
        return fs.mkdir(path, onDone);
      }

      if (entry.type === 'blob') {
        return fs.writeFile(path, entry.body, onDone);
      }

      return read(onEntry);
    }

    function onDone(err) {
      if (err) return cb(err);
      return read(onEntry);
    }
  });
}