Error on using express module in node js

Question

I am a newbie in node.js. I am using the following code. I have installed the express module and the related files have been installed.

var express = require('express')
var app = express.createServer()
app.listen(8000)

var tweets = []

app.get('/', function(req, res) {
  res.send('Welcome to Node Twitter')
})

app.post('/send', express.bodyParser(), function(req, res) {
  if (req.body && req.body.tweet) {
    tweets.push(req.body.tweet)
    res.send({status:"ok", message:"Tweet received"})
  } else {
    //no tweet?
    res.send({status:"nok", message:"No tweet received"})
  }
})

app.get('/tweets', function(req,res) {
  res.send(tweets)
})

I am getting the following error.

 var app = function(req, res, next) {
   app.handle(req, res, next);
 };

 mixin(app, proto);
 mixin(app, EventEmitter.prototype);

 app.request = { __proto__: req, app: app };
 app.response = { __proto__: res, app: app };
 app.init();
 return app;
 has no method 'createServer'
   at Object.<anonymous> (D:\ProgramFiles\Nodejs\node_modules\twitter.js:3:19)
   at Module._compile (module.js:456:26)
   at Object.Module._extensions..js (module.js:474:10)
   at Module.load (module.js:356:32)
   at Function.Module._load (module.js:312:12)
   at Function.Module.runMain (module.js:497:10)
   at startup (node.js:119:16)
   at node.js:906:3

This happens when I place the file outside the modules folder. When I place it somewhere else, it cant find the module also and returns the following error.

module.js:340
    throw err;
          ^
Error: Cannot find module 'express'
    at Function.Module._resolveFilename (module.js:338:15)
    at Function.Module._load (module.js:280:25)
    at Module.require (module.js:364:17)
    at require (module.js:380:17)
    at Object.<anonymous> (D:\NodeApp\twitter.js:1:77)
    at Module._compile (module.js:456:26)
    at Object.Module._extensions..js (module.js:474:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:312:12)
    at Function.Module.runMain (module.js:497:10)

How to resolve this?

AAAH. You are using a newer version of express which only might need var app = express(); Check your version of express :) — Joakim M
– Joakim M, Commented Jun 18, 2014 at 10:28

Matthew Bakaitis · Accepted Answer · 2014-06-18 18:20:04Z

Assuming a new version of express as @JoakimM suggested in comments, you would want to:

update the var app = express() declaration to use the new syntax
npm install body-parser --save to get the new body-parser middleware that no longer comes with Express 4.0 ( see: migrating from 3.x to 4.x docs)
add a declaration to require the new middleware
add app.use so that express knows about the new middleware
remove the express.bodyparser argument from app.post('/send' route
moved app.listen to the bottom. maybe this is superstition...but that's where I put it.
I know this is grounds for a flamewar, but semicolons are your friend :) :) :)

Results of the above, worked on my system:

var express = require('express')
var bodyParser = require('body-parser')
var app = express()

var tweets = []

app.use(bodyParser())

app.get('/', function(req, res) {
  res.send('Welcome to Node Twitter')
})

app.post('/send', function(req, res) {
  if (req.body && req.body.tweet) {
    tweets.push(req.body.tweet)
    res.send({status:"ok", message:"Tweet received"})
  } else {
    //no tweet?
    res.send({status:"nok", message:"No tweet received"})
  }
})

app.get('/tweets', function(req,res) {
  res.send(tweets)
})

app.listen(8000)

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