The error message "app.listen is not a function" is indicating that there

I am encountering an issue while trying to start my server from the www file. The error message I receive is as follows. Can anyone help me understand why this error is occurring?

The version of Express I am using is 4.16. Could it be related to a problem with the node environment path? Or could there be another underlying issue causing this?

❯ ./bin/www                                                                               ✔ master
/Users/me/Test/ExpressAPP/bin/www:6
app.listen(3000, function () {
    ^

TypeError: app.listen is not a function
    at Object.<anonymous> (/Users/me/Test/ExpressAPP/bin/www:6:5)
    at Module._compile (module.js:624:30)
    ... (additional stack trace omitted for brevity) ...

./bin/www

#!/usr/bin/env node

var app = require('./../app')

app.listen(3000, function(){
    console.log('Listening on port 300')
})

app.js

var express = require('express')
var app = express()

app.get('/', function(request, response){
    response.send('OK')
})

module.exports = app

Answer №1

It seems like there shouldn't be any issues with your code. I actually tested a demo using your code snippet, and it worked perfectly fine. The problem might be related to your specific environment. Have you tried deleting the node_modules folder and re-installing npm packages using the npm i -S express command?

I also have a couple of suggestions that could help you resolve your problem.

  • Try adding console.log(app) in the www file to see if the app object being required is the same as the one you created in app.js.
  • Double-check your source code to ensure it matches exactly what you have pasted, especially focusing on the module.exports = app line. Sometimes small errors like missing characters can make a big difference.

Answer №2

Give this code a try:

/* config/express.js */
var express = require('express');
module.exports = function() {
  var app = express();
  app.set('port', 3000);
  return app;
};


/* server.js */
var http = require('http');
var app = require('./config/express')(); // Don't forget the extra ()
  
http.createServer(app).listen(app.get('port'), function() {
    console.log("Server is running on port: "+ app.get('port'));
});

Answer №3

I encountered a similar problem:

incorrect: module.export=app;  

 correct: module.exports=app; 

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