how to run node.js app from cmd with some predefined port in Windows

On ubuntu I just do

PORT=7777 node .

in commandline, no set or export needed.

Depending on what server.js contains you should be able to do so.

At a minimum you should read port (you could use https://github.com/substack/node-optimist)

var argv = require('optimist').argv;
console.log(argv.port);

// use it like this
$ node server.js -port 7777

and then listen to it on your server (this depends on what lib you're using).

Run the server like this

export PORT=7777; node server.js

A simple adding to Alberto's answer. On Windows machine you haven't export command in cmd, use set instead. Then the whole script will be looks like this:

set PORT=7777
node server.js

Note that the syntax in PowerShell is slightly different:

$env:PORT=7777
node server.js