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>;

This function:

• Takes an optional Options parameter
• Returns a Promise that resolves to a number (the available port)

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

• port: a preferred port or iterable of ports
• exclude: ports to exclude from consideration
• reserve: whether to lock the port for the process lifetime
• host: the specific host to check availability on

FOLLOW_UPS:

• What does the reserve option do exactly?
• How does the exclude option work?
• What is the portNumbers helper function?