title: Route.get() requires callback functions but got a "object Undefined"
body: <p>I am learning making Todo app.
  On the website, I am studying is <a href="https://coderwall.com/p/4gzjqw/build-a-javascript-todo-app-with-express-jade-and-mongodb" rel="noreferrer">https://coderwall.com/p/4gzjqw/build-a-javascript-todo-app-with-express-jade-and-mongodb</a></p>
  <p>I typed as instruction describes,</p>
  <p><strong>app.js</strong></p>
  <pre class="lang-js prettyprint-override"><code>var main = require('./routes/main');
  var todo = require('./routes/todo');
  var todoRouter = express.Router();
  app.use('/todos', todoRouter);
  app.get('/', main.index);
  todoRouter.get('/',todo.all);
  todoRouter.post('/create', todo.create);
  todoRouter.post('/destroy/:id', todo.destroy);
  todoRouter.post('/edit/:id', todo.edit);
  </code></pre>
  <p><strong>/routes/todo.js</strong></p>
  <pre class="lang-js prettyprint-override"><code>module.exports ={
    all: function(req, res){
      res.send('All todos');
    },
    viewOne: function(req, res){
      console.log('Viewing '+req.params.id);
    },
    create: function(req, res){
      console.log('Todo created');
    },
    destroy: function(req, res){
      console.log('Todo deleted');
    },
    edit: function(req, res){
      console.log('Todo '+req.params.id+' updated');
    }
  };
  </code></pre>
  <p>and I got this error message</p>
  <blockquote>
  <p>Error: Route.get() requires callback functions but got a [object
  Undefined]</p>
  </blockquote>
  <p>Did I miss something here?</p>