title: Create user, callback
body: <p>1st post. I'm a student studying js and came across this problem with a callback that I'm not sure how to structure properly.</p>
  
  <pre><code>var bcrypt = require('bcrypt-nodejs');
  var users = db.collection("users");
  this.addUser = function(username, password, email, callback) {
      "use strict";
  
      // Generate password hash
      var salt = bcrypt.genSaltSync();
      var password_hash = bcrypt.hashSync(password, salt);
  
      // Create user document
      var user = {'_id': username, 'password': password_hash};
  
      // Add email if set
      if (email != "") {
          user['email'] = email;
      }
  
      // NOT SURE What to write here
      callback(Error("addUser Not Yet Implemented!"), null);
  
  }
  </code></pre>