get-port 
Get an available TCP port
Install
$ npm install get-port
Usage
const getPort = require('get-port');
(async () => {
console.log(await getPort());
//=> 51402
})();
Pass in a preferred port:
(async () => {
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:
(async () => {
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 makeRange() helper in case you need a port in a certain range:
(async () => {
console.log(await getPort({port: getPort.makeRange(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.
host
Type: string
The host on which port resolution should be performed. Can be either an IPv4 or IPv6 address.
getPort.makeRange(from, to)
Make a range of ports from...to.
Returns an Iterable for ports in the given range.
from
Type: number
First port of the range. Must be in the range 1024...65535.
to
Type: number
Last port of the range. Must be in the range 1024...65535 and must be greater than from.
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