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.

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

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 removes protection against in-process 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.

In-process race conditions (such as when running parallel Jest tests) are completely eliminated by a lightweight locking mechanism where returned ports are held for 15-30 seconds before being eligible for reuse.

Multi-process race conditions are extremely rare and will result in an immediate EADDRINUSE error when attempting to bind to the port, allowing your application to retry.

Related

• get-port-cli - CLI for this module