get-port

What is get-port?

The get-port npm package is designed to help developers find an available port on the machine where their code is running. This can be particularly useful in development environments where specific ports may already be in use, or when deploying applications that need to dynamically select an available port to avoid conflicts.

What are get-port's main functionalities?

Get an available port

This basic usage of get-port allows you to asynchronously retrieve an available port on the system. The function `getPort()` returns a Promise that resolves to a port number that is currently free on the host machine.

const getPort = require('get-port');

(async () => {
  console.log(await getPort());
})();

Specify a preferred port

With get-port, you can also specify a preferred port. If the preferred port is available, it will be returned. Otherwise, get-port will find and return another available port. This is useful when you have a default port for your application but need to automatically switch if it's in use.

const getPort = require('get-port');

(async () => {
  console.log(await getPort({port: 3000}));
})();

Get an available port from a range

This feature allows you to specify a range of ports, and get-port will return the first available port from that range. This is particularly useful when you want to limit the ports your application might use to a specific subset.

const getPort = require('get-port');

(async () => {
  console.log(await getPort({port: [3000, 3001, 3002]}));
})();

Other packages similar to get-port

portfinder

Portfinder is a similar package that helps in getting an available port. Unlike get-port, portfinder starts at a given port and increments until an open port is found. It provides more control over the starting port but doesn't support specifying preferred ports or ranges directly.

find-free-port

This package also aims to find a free port on the host machine. It differs from get-port by allowing users to specify a start and end port, effectively searching for a free port within a given range. It's more focused on range-based searches compared to get-port's more flexible options.

README

get-port

Get an available TCP port.

Install

npm install get-port

Usage

import getPort from 'get-port';

console.log(await getPort());
//=> 51402

Pass in a preferred port:

import getPort from 'get-port';

console.log(await getPort({port: 3000}));
// Will use 3000 if available, otherwise fall back to a random port

Pass in an array of preferred ports:

import getPort from 'get-port';

console.log(await getPort({port: [3000, 3001, 3002]}));
// Will use any element in the preferred ports array if available, otherwise fall back to a random port

Use the portNumbers() helper in case you need a port in a certain range:

import getPort, {portNumbers} from 'get-port';

console.log(await getPort({port: portNumbers(3000, 3100)}));
// Will use any port from 3000 to 3100, otherwise fall back to a random port

API

getPort(options?)

Returns a Promise for a port number.

options

Type: object

port

Type: number | Iterable<number>

A preferred port or an iterable of preferred ports to use.

exclude

Type: Iterable<number>

Ports that should not be returned.

You could, for example, pass it the return value of the portNumbers() function.

host

Type: string

The host on which port resolution should be performed. Can be either an IPv4 or IPv6 address.

By default, it checks availability on all local addresses defined in OS network interfaces. If this option is set, it will only check the given host.

portNumbers(from, to)

Generate port numbers in the given range from...to.

Returns an Iterable for port numbers in the given range.

from

Type: number

The first port of the range. Must be in the range 1024...65535.

to

Type: number

The last port of the range. Must be in the range 1024...65535 and must be greater than from.

clearLockedPorts()

Clear the internal cache of locked ports.

This can be useful when you want the results to be unaffected by previous calls.

Please note that clearing the cache could cause race conditions.

import getPort, {clearLockedPorts} from 'get-port';

const port = [3000, 3001, 3002];

console.log(await getPort({port}));
//=> 3000

console.log(await getPort({port}));
//=> 3001

// If you want the results to be unaffected by previous calls, clear the cache.
clearLockedPorts();

console.log(await getPort({port}));
//=> 3000

Beware

There is a very tiny chance of a race condition if another process starts using the same port number as you in between the time you get the port number and you actually start using it.

Race conditions in the same process are mitigated against by using a lightweight locking mechanism where a port will be held for a minimum of 15 seconds and a maximum of 30 seconds before being released again.

Related

• get-port-cli - CLI for this module