express app server . listen all interfaces instead of localhost only

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)

From the documentation: app.listen(port, [hostname], [backlog], [callback])

Binds and listens for connections on the specified host and port. This method is identical to Node’s http.Server.listen().

var express = require('express');
var app = express();
app.listen(3000, '0.0.0.0');

document: app.listen([port[, host[, backlog]]][, callback])

example:

const express = require('express');
const app = express();
app.listen('9000','0.0.0.0',()=>{
      console.log("server is listening on 9000 port");
})

Note: 0.0.0.0 to be given as host in order to access from outside interface