javascript - express app server . listen all interfaces instead of localhost only

Question

I'm very new for this stuff, and trying to make some express app

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

app.listen(3000, function(err) {
    if(err){
       console.log(err);
       } else {
       console.log("listen:3000");
    }
});

//something useful
app.get('*', function(req, res) {
  res.status(200).send('ok')
});

When I start the server with the command:

node server.js 

everything goes fine.

I see on the console

listen:3000

and when I try

curl http://localhost:3000

I see 'ok'.

When I try

telnet localhost

I see

Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]' 

but when I try

netstat -na | grep :3000

I see

tcp  0  0 0.0.0.0:3000   0.0.0.0:*  LISTEN

The question is: why does it listen all interfaces instead of only localhost?

The OS is linux mint 17 without any whistles.

Answer 1

If you use don't specify host while calling app.listen, server will run on all interfaces available i.e on 0.0.0.0

You can bind the IP address using the following code

app.listen(3000, '127.0.0.1');

If you want to run server in all interface use the following code

app.listen(3000, '0.0.0.0');

or

app.listen(3000)