javascript - Unable to map routes file with ExpressJS Router -

I am reading an introduction book about ExpressJS and unfortunately they are using Express 3.x. I'm trying to update my code to express example 4.x. Here's an example:

route / index.js

  export.index = function (req, res) {res.send (' Welcome'); };   
  app.js   
  var express = expected ('express'); Var http = Required ('http'); Var app = express (); // Load the root handlers requires different routes ('./routes'); // router middleware explicitly add app.use (app.router); // roots app.get ('/', routes.index); Http.createServer (app) .listen (3000, function () {console.log ('app start');});   
 Here,  app.router  dislikes and the node throws an error about it I updated the code:  
  Var http = Required ('http'); Var Express = Required ('Express'); Var app = express (); Var bodyParser = is required ('body-parser'); Var router = express.routor (); Var routes are required ('./routes'); Router.get ('/', routes.inx); App.use (bodyParser.urlencoded ({extended: true})); App.use (bodyParser.json ()); Http.createServer (app) .listen (3000, function () {console.log ('Express app start');});   
 However, when going to  localhost: 3000 , I see this error in the browser:  
  can not be found /   
 If I completely use the router class (and remove  app.router) ), then just do this I can:  
  app.get ('/', routes .indack);   
 And that will work.  
 How do I load my outer path with the router class?   
 
 
 In Express 4, you create your own path using the router.  
 Say, your route / index.js and path / foo.js, they will see something like this:  
  // path / index.js var router = Required ('Express'). Router (); Router.get ('/', function (rik, ridge) {res.send ('hello!');}); Module.exports = Router; Requires the   
  // path / foo.js var router = ('Express'). Router (); Router.get ('/ bar', function (rik, ridge) {res.send ('foobar');}); Module.exports = Router;   
 In your main server file, you can use these router app, you can attach them to different places. You can also make router to attach the router to the router (for example, the user / user-id / picture / image-id type route).  
  // server.js var http = require ('http'); Var Express = Required ('Express'); Var app = express (); Var bodyParser = is required ('body-parser'); App.use ('/', is required ('. / Route / index')); App.use (bodyParser.urlencoded ({extended: true})); App.use (bodyParser.json ()); App.use ('/ foo', Required ('./routes / foo')); App.listen (3000);   
 and now you should be able to get GET / and GET / foo / bar.  
 
 For a little more technical accuracy, you need middleware only on routes.  
 You can make this per router, or per-end point.  
  router.use (bodyParser.json ()); // router.route ('/ baz') .use (bodyParser.json ()) .post (function (rik, ridge) {res.status (201) .json (req.body);});   
 It is usually good to do, but in some cases it may also be very important, e.g. Handling file uploads