interface IUser {
  username: string;
  pass: string;
  id: number;
}

type IPartial<TObject> = {
  [property in keyof TObject]?: TObject[property];
}

class User<TParams> {
  constructor(private params: IPartial<TParams>) {

  }

  public set<TKey extends keyof TParams>(key: TKey, value: TParams[TKey]): void;
  public set(params: IPartial<TParams>): void;
  public set(key? :any, value?: any): void {
    if (typeof key === 'string') {
      this.params[key as keyof TParams] = value;
      return;
    }
    else if (typeof key === 'object') {
      const params = key as IPartial<TParams>;

      for (let paramKey in params) {
        this.set(paramKey, params[paramKey]);
      }

      return;
    }
    else {
      throw new TypeError('func up');
    }
  }

  public get<TKey extends keyof TParams>(key: TKey): TParams[TKey] {
    return this.params[key];
  }
}

const usr = new User<IUser>({
  pass: '123'
});

usr.set('pass', '123');
usr.set('id', 1);

usr.set({
  pass: 'google'
})