Is it correct to throw an Error inside the catch block?-CodePudding

I'm writing a middleware that has a services layer and a controller layer. In order to transmit a clear error message to the user, I catch any errors in the services layer and then throw a new Error with a personalized message, like this:

// services.js
  async getOneRecord(id) {
    const url = this.url   `/${id}`;
    return await axios.get(url).then((res) => res.data);
  }

// UserServices.js
    async getTaxValue(id) {
    try {
      const user = await this.getOneRecord(id);
      return Number(user.tax) / 100;
    } catch (error) {
      throw new Error(`User ID not found: ${id}`);
    }
  }

// UserController.js
  static async getUserTax(req, res) {
    const { userId } = req.params;

    try {
      const user = await userServices.getTaxValue(userId);
      return res.status(200).json(user);
    } catch (error) {
      return res.status(404).json(error.message);
    }
  }

I would like to find out if this is the right way to treat errors or if I'm doing something wrong.

CodePudding user response：

Yes, it's correct and normal to throw new errors in catch blocks.

However, it is not a good practice to ignore the error that you caught. There are a lot of things that can go wrong in getTaxValue, and I would argue that most of them should not result in an "id not found" error. So be very explicit about the error that you expect, test for it with a condition, and rethrow everything else unchanged. Also set the .cause of errors.

In your case, that might be (handling only 404 errors from the user record endpoint):

class NotFoundError extends Error {}

async getTaxValue(id) {
  try {
    const user = await this.getOneRecord(id);
    return Number(user.tax) / 100;
  } catch (error) {
    if (error.response && error.response.status == 404) { // see AxiosError
      throw new NotFoundError(`User ID not found: ${id}`, {cause: error});
    }
    throw error;
  }
}

// UserController.js
async function getUserTax(req, res) {
  const { userId } = req.params;
  try {
    const user = await userServices.getTaxValue(userId);
    return res.status(200).json(user);
  } catch (error) {
    return res.status(error instanceof NotFoundError ? 404 : 500).json(error.message);
  }
}