Method watch

src/pkg/config/config.ts:114–124

(
    key: T,
    callback: (value: SystemConfigValueType<T>, prev: SystemConfigValueType<T> | undefined) => void
  )

  // 监听配置变更，会使用设置值立即执行一次回调
  watch<T extends SystemConfigKey>(
    key: T,
    callback: (value: SystemConfigValueType<T>, prev: SystemConfigValueType<T> | undefined) => void
  ) {
    // 立即执行一次
    this.get(key).then((val) => {
      callback(val, undefined);
    });
    // 监听变更
    return this.addListener(key, callback);
  }

  private resolveDefault<T>(defaultValue: WithAsyncValue<Exclude<T, undefined>>): T | Promise<T> {
    //@ts-ignore