class Config {
  constructor(options = {}) {
    this.retries = options.retries ?? 3;
    this.timeout = options.timeout ?? 1000;
  }
}
const cfg1 = new Config({ retries: 0, timeout: null });
const cfg2 = new Config({ retries: undefined, timeout: false });
cfg1.retries ??= 99;
cfg2.timeout ??= 99;
console.log(cfg1.retries, cfg1.timeout, cfg2.retries, cfg2.timeout);