One liner to create a Node.js HTTP server:

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require('http').createServer((req, res) => res.end('OK')).listen(3000);

Also see the previous one liners for older Node.js versions.

One liner to create a Node.js HTTP server:

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require('http').createServer(function (req, res) { res.end('OK'); }).listen(3000);

Print out the process ID instead:

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require('http').createServer(function (req, res) { res.end('' + process.pid); }).listen(3000);

This is useful with the worker process when implementing the cluster module.

This is a bare minimal HTTP server:

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require('http').createServer().listen(port);

If the port number is evaluated to be falsy, such as 0, null, undefined or an empty string, a random port will be assigned.

Begin accepting connections on the specified port and hostname. If the hostname is omitted, the server will accept connections on any IPv6 address (::) when IPv6 is available, or any IPv4 address (0.0.0.0) otherwise. A port value of zero will assign a random port. - https://iojs.org/api/http.html#http_server_listen_port_hostname_backlog_callback

We can use command line tool such as netstat to find out the port number:

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$ netstat -ltpn | grep node
tcp6     0    0 :::44055             :::*            LISTEN      5624/node

However, it will be very convenient without relying on external tools.

Luckily, we can find out the port number by using the address method:

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require('http').createServer().listen().address()

The result will be similar to:

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{ address: '::', family: 'IPv6', port: 44055 }

Furthermore, it works with all popular libraries that create an http.Server instance: