Is there a helper to generate a sequence of port numbers to try?

Yes, there is. The portNumbers() helper function generates a sequence of port numbers in a given range.

According to [index.js:L169-L194], the portNumbers(from, to) function generates port numbers from from to to (inclusive) and returns an iterable:

export function portNumbers(from, to) {
	if (!Number.isInteger(from) || !Number.isInteger(to)) {
		throw new TypeError('`from` and `to` must be integer numbers');
	}

	if (from < minPort || from > maxPort) {
		throw new RangeError(`'from' must be between ${minPort} and ${maxPort}`);
	}

	if (to < minPort || to > maxPort) {
		throw new RangeError(`'to' must be between ${minPort} and ${maxPort}`);
	}

	if (from > to) {
		throw new RangeError('`to` must be greater than or equal to `from`');
	}

	const generator = function * (from, to) {
		for (let port = from; port <= to; port++) {
			yield port;
		}
	};

	return generator(from, to);
}

Both from and to must be integers in the range 1024...65535, and to must be greater than or equal to from. You can use it with getPort() by passing it to the port option [index.d.ts:L5]:

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

FOLLOW_UPS:

• What validation does portNumbers() perform?
• Can I exclude specific ports from consideration?
• How does getPort handle port preference ordering?