NodeJS: How to get the server's port?

Question

You often see example hello world code for Node that creates an Http Server, starts listening on a port, then followed by something along the lines of:

console.log('Server is listening on port 8000');

But ideally you'd want this instead:

console.log('Server is listening on port ' + server.port);

How do I retrieve the port the server is currently listening on without storing the number in a variable prior to calling server.listen()?

I've seen this done before but I can't find it in the Node documentation. Maybe it's something specific to express?

Rockwood

Find in req.headers.host – Radley

Answer 1

Express 4.x answer:

Express 4.x (per Tien Do's answer below), now treats app.listen() as an asynchronous operation, so listener.address() will only return data inside of app.listen()'s callback:

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

var listener = app.listen(8888, function(){
    console.log('Listening on port ' + listener.address().port); //Listening on port 8888
});

Express 3 answer:

I think you are looking for this(express specific?):

console.log("Express server listening on port %d", app.address().port)

You might have seen this(bottom line), when you create directory structure from express command:

alfred@alfred-laptop:~/node$ express test4
   create : test4
   create : test4/app.js
   create : test4/public/images
   create : test4/public/javascripts
   create : test4/logs
   create : test4/pids
   create : test4/public/stylesheets
   create : test4/public/stylesheets/style.less
   create : test4/views/partials
   create : test4/views/layout.jade
   create : test4/views/index.jade
   create : test4/test
   create : test4/test/app.test.js
alfred@alfred-laptop:~/node$ cat test4/app.js 

/**
 * Module dependencies.
 */

var express = require('express');

var app = module.exports = express.createServer();

// Configuration

app.configure(function(){
  app.set('views', __dirname + '/views');
  app.use(express.bodyDecoder());
  app.use(express.methodOverride());
  app.use(express.compiler({ src: __dirname + '/public', enable: ['less'] }));
  app.use(app.router);
  app.use(express.staticProvider(__dirname + '/public'));
});

app.configure('development', function(){
  app.use(express.errorHandler({ dumpExceptions: true, showStack: true })); 
});

app.configure('production', function(){
  app.use(express.errorHandler()); 
});

// Routes

app.get('/', function(req, res){
  res.render('index.jade', {
    locals: {
        title: 'Express'
    }
  });
});

// Only listen on $ node app.js

if (!module.parent) {
  app.listen(3000);
  console.log("Express server listening on port %d", app.address().port)
}

Tardiff

Thanks, I think that's exactly what I'm looking for. I'll accept it as soon as I get a chance to test it. Cheers. – Rockwood

And if you don't want to have that variable var listener you can use this.address().port inside app.listen() callback – Kinelski

What does this look like in Express 5.x? – Department

You can also get the port anywhere in a middleware : req.socket.address().port – Builtup

Just to add on to what @AndreiStalbe said, you can use this.address.port() but you cannot use that inside an arrow function. you will need to do old school app.listen(8000, function () { console.log('http://localhost:' + this.address().port); } (yes, I know backticks are nicer, but I can't do them in stack overflow comments) – Hoatzin

listener.address doesn't work when I try to run it from inside an async function, not sure why. Express 4.17.1, Node v14.17.0. – Denticulation

Answer 2

In express v3.0,

/* No longer valid */
var app = express.createServer();
app.listen();
console.log('Server running on %s', app.address().port);

no longer works! For Express v3.0, you should create an app and a server this way:

var express = require('express');
var http = require('http');

var app = express();
var server = http.createServer(app);

app.get('/', function(req, res) {
    res.send("Hello World!");
});

server.listen(3000);
console.log('Express server started on port %s', server.address().port);

I ran in to this issue myself and wanted to document the new syntax. This and other changes in Express v3.0 are visible at https://github.com/visionmedia/express/wiki/Migrating-from-2.x-to-3.x

Maciemaciel

Or you could just use the old method of creating the server, which still works. There just seems to no longer be a way to access the port afterword. However, since you are specifying the port yourself in the call to server.listen, there really isn't a need to use server.address().port, since you can just use the same value that you passed into server.listen. – Journeywork

(Although I did just read the migration guide and see that the method for creating an app and server that you mentioned above is actually the new preferred method.) – Journeywork

@MaryHamlin: This is useful if you are passing 0 to server.listen(), in which case a random port number is assigned. You might do this if you’re running several Express apps on one server and you don’t want to manually assign port numbers. – Faxun

app.listen() also returns the http server instance. – Gadfly

Answer 3

In case when you need a port at the time of request handling and app is not available, you can use this:

request.socket.localPort

Crease

This is the answer! :) – Cordalia

Answer 4

In the current version (v0.5.0-pre) the port seems to be available as a property on the server object, see http://nodejs.org/docs/v0.4.7/api/net.html#server.address

var server = http.createServer(function(req, res) {
    ...
}

server.listen(8088);
console.log(server.address());
console.log(server.address().address);
console.log(server.address().port);

outputs

{ address: '0.0.0.0', port: 8088 }
0.0.0.0
8088

Marcellemarcellina

Answer 5

I use this way Express 4:

app.listen(1337, function(){
  console.log('Express listening on port', this.address().port);
});

By using this I don't need to use a separate variable for the listener/server.

Mims

Best answer so far! If you are using ES6 do not use arrow-functions. this will be undefined. – Felipa

This works from inside an async function while listener.address().port approach didn't. – Denticulation

Answer 6

If you're using express, you can get it from the request object:

req.app.settings.port // => 8080 or whatever your app is listening at.

Transcendentalistic

Answer 7

Requiring the http module was never necessary.

An additional import of http is not necessary in Express 3 or 4. Assigning the result of listen() is enough.

var server = require('express')();

server.get('/', function(req, res) {
  res.send("Hello Foo!");
});

var listener = server.listen(3000);
console.log('Your friendly Express server, listening on port %s', listener.address().port);
// Your friendly Express server, listening on port 3000

Again, this is tested in Express 3.5.1 & 4.0.0. Importing http was never necessary. The listen method returns an http server object. https://github.com/visionmedia/express/blob/master/lib/application.js#L531

Christlike

Answer 8

If you did not define the port number and you want to know on which port it is running.

let http = require('http');
let _http = http.createServer((req, res) => {
res.writeHead(200);
res.end('Hello..!')
}).listen();
console.log(_http.address().port);

FYI, every time it will run in a different port.

Stone

Answer 9

req.headers.host.split(':')[1]

Persiflage

Answer 10

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

app.set('port', Config.port || 8881);

var server = app.listen(app.get('port'), function() {
    console.log('Express server listening on port ' + server.address().port); 
});

Express server listening on port 8881

Colfin

Answer 11

You can get the port number by using server.address().port like in below code:

var http = require('http');
var serverFunction = function (req, res) {

    if (req.url == '/') {
        console.log('get method');
        res.writeHead(200, { 'content-type': 'text/plain' });
        res.end('Hello World');
    }

}
var server = http.createServer(serverFunction);
server.listen(3002, function () {
    console.log('server is listening on port:', server.address().port);
});

Libation

Answer 12

With latest node.js (v0.3.8-pre): I checked the documentation, inspected the server instance returned by http.createServer(), and read the source code of server.listen()...

Sadly, the port is only stored temporarily as a local variable and ends up as an argument in a call to process.binding('net').bind() which is a native method. I did not look further.

It seems that there is no better way than keeping a reference to the port value that you provided to server.listen().

Upshaw

+1 and thanks for the research. I'm accepting Alfred's answer since he found the exact thing I was looking for, but I'm glad I know it's not in the Node core now. – Rockwood

Answer 13

The simplest way to convert from the old style to the new (Express 3.x) style is like this:

var server = app.listen(8080);
console.log('Listening on port: ' + server.address().port);

Pre 3.x it works like this:

/* This no longer works */
app.listen(8080);
console.log('Listening on port: ' + app.address().port);

Anecdote

Answer 14

I was asking myself this question too, then I came Express 4.x guide page to see this sample:

var server = app.listen(3000, function() {
   console.log('Listening on port %d', server.address().port);
});

Audra

But I don't know why server.address().address is always 0.0.0.0 on my local development machine (OSX). – Audra

This should be added to the accepted answer since Express 4.0 no longer treats app.listen() as a synchronous operation and you need to run listener.address() in the callback now. – Carmacarmack

Answer 15

The findandbind npm addresses this for express/restify/connect: https://github.com/gyllstromk/node-find-and-bind

Isocline

Answer 16

const express = require('express');                                                                                                                           
const morgan = require('morgan')
const PORT = 3000;

morgan.token('port', (req) => { 
    return req.app.locals.port; 
});

const app = express();
app.locals.port = PORT;
app.use(morgan(':method :url :port'))
app.get('/app', function(req, res) {
    res.send("Hello world from server");
});

app1.listen(PORT);

Resplendent

Answer 17

You might be looking for process.env.PORT. This allows you to dynamically set the listening port using what are called "environment variables". The Node.js code would look like this:

const port = process.env.PORT || 3000; 
app.listen(port, () => {console.log(`Listening on port ${port}...`)}); 

You can even manually set the dynamic variable in the terminal using export PORT=5000, or whatever port you want.

Triadelphous

Answer 18

express v4+

const app = require("express")();
app.listen( 5555, function() {
  console.log( this.address().port )
})

Oregon

Your answer could be improved by adding more information on what the code does and how it helps the OP. – Kweisui

Answer 19

Using express

const express = require("express")
const app=express();
app.listen(3000, ()=>{
console.log("Listening to post 3000");
}
using HTTP
const http=require('http');

const server = http.createServer((req, res), ()=>{
res.end("am server")
})
server.listen(3000, ()=>{
console.log("Listening to post 3000");
})

Acromion

Please note that this is not an answer. You wrote a snippet to start a Node JS server with Express on Port 3000. That is not what was asked. – Larimor

Answer 20

The easier way is just to call app.get('url'), which gives you the protocol, sub domain, domain, and port.

Forwardness