node-portfinder 
Installation
$ [sudo] npm install portfinder
Usage
The portfinder module has a simple interface:
var portfinder = require('portfinder');
portfinder.getPort(function (err, port) {
//
// `port` is guaranteed to be a free port
// in this scope.
//
});
Or with promise (if Promise are supported) :
const portfinder = require('portfinder');
portfinder.getPortPromise()
.then((port) => {
//
// `port` is guaranteed to be a free port
// in this scope.
//
})
.catch((err) => {
//
// Could not get a free port, `err` contains the reason.
//
});
If portfinder.getPortPromise() is called on a Node version without Promise (<4), it will throw an Error unless Bluebird or any Promise pollyfill is used.
Ports search scope
By default portfinder will start searching from 8000 and scan until maximum port number (65535) is reached.
You can change this globally by setting:
portfinder.basePort = 3000; // default: 8000
portfinder.highestPort = 3333; // default: 65535
or by passing optional options object on each invocation:
portfinder.getPort({
port: 3000, // minimum port
stopPort: 3333 // maximum port
}, callback);
Run Tests
$ npm test