node.js error of callback function in

I am facing an error in my node.js code.

Error: /workspace/Ap/node_modules/express/lib/router/index.js:252
throw new Error(msg);
      ^
Error: .get() requires callback functions but got a [object Undefined].

Yesterday my code was working fine but today with same code i face above error, and I don't get where is the problem. My code is:

 app.js

 var express = require('express');

 var routes = require('./routes');

 var http = require('http');

 var path = require('path');

 var app = express();

 var mysql = require('mysql');

routes/index.js

module.exports = function(req, res){

  res.render('index', { title: 'Express' });

};

Thanks..