What is the type signature of the main exported function?

The main exported function getPort has the following type signature [index.d.ts:L66]:

export default function getPort(options?: Options): Promise<number>;

It accepts an optional Options object and returns a Promise that resolves to a port number.

The Options type is defined in [index.d.ts:L3-L65] and includes:

• port: A preferred port or iterable of preferred ports
• exclude: Ports that should not be returned
• reserve: Boolean to lock the port for the process lifetime (default: false)
• host: A specific host (IPv4 or IPv6) to check port availability on

FOLLOW_UPS:

• What does the reserve option do exactly?
• How does the exclude option work with portNumbers()?
• What happens when all preferred ports are unavailable?