❗️Что будет на выходе:

const config = {
  port: 0,
  timeout: null,
  retries: '',
  cache: false,
  debug: undefined
};

const port = config.port ?? 3000;
const timeout = config.timeout ?? 5000;
const retries = config.retries ?? 3;
const cache = config.cache ?? true;
const debug = config.debug ?? false;

console.log([port, timeout, retries, cache, debug]);

Ответ:
[0, 5000, '', false, false]

JavaScript test | #JavaScript