title: Why "TypeError: express.Router is not a function"
body: <p>Trying to make a login app with nodejs express.
  However after I run it. it shows TypeError: express.Router is not a function.
  My express is the latest version4.13.4. Can anyone help me?Here is the code.</p>
  
  <pre><code>var User = require('../modules/user');
  var config = require('../../config');
  
  var secretKey = config.secretKey;
  
  module.exports = function(app,express){
      var api = express.Router;
      api.post('/signup', function(req,res){
          var user = new User({
              name: req.body.name,
              username: req.body.username,
              password: req.body.password
          });
  
          user.save(function(err){
              if(err){
                  res.send(err);
                  return;
              }
  
              res.json({ message: 'user has been created'});
          })
      });
  
      return api;
  };
  </code></pre>