错误处理：如何在我的前端接收来自我的后端的错误消息？

Question

I'm building my first full stack application, and I'm having problem with error handling on my backend, I also don't know how to receive this error message on my frontend.

Here is how my application is working: (I'm using nodejs, express.js, mongodb and react)

 // 1. I got a form where user provide some data. 
 // 2. Redux action creator is sending this data to my API.
 // 3. Basing on this data, my API is fetching other API for some information.
 // 4. And the response is pushed to my data base, and then send back to my reducer, and it's in my store. 

Thing is, that before I push the response to my database I want to check if this item exists in the API that I'm fetching on the backend, and if not then I want to receive this kind of message, and display that to my user just below the form.

Here is my action creator on frontend:

export const addTransaction = (transaction) => async (dispatch) => {
  try {
    const { data } = await api.addTransaction(transaction);

    dispatch({
      type: ADD_TRANSACTION,
      payload: data
    });
  } catch (error) {
    console.log(error.message);
  };
};

And here is my backend controller:

export const addTransaction = async (req, res) => {
  const transaction= req.body

  const myUpdatedTransaction = {
    ...transaction,
    someOther: "fields"
  };

  const requestOptions = {/*GET, url, api_key, etc. */},

// here is where I'm trying to handle this case

  await request(requestOptions).then( async (resolve) => {

    if(resolve) { 

      const newTransaction = new TransactionItem(myUpdatedTransaction) 
      
      await newTransaction.save();

      res.status(201).json(newTransaction);

      return;
    }

  }, (err) => {
    /******** And here where I don't know how to deal with this *******/
    console.log('error ----->');

    if(err) {
      res.status(409).json({ message: 'Check if the ticker is correct.'});
      console.log('409');

      return;
    }

  });

};

I will appreciate if someone can share some links where I can learn more about error handling.

Answer 1

Well it looks like you're mixing up two concepts.

https://www.smashingmagazine.com/2020/11/comparison-async-await-versus-then-catch/

export const addTransaction = async (req, res) => {
  const transaction= req.body

  const myUpdatedTransaction = {
    ...transaction,
    someOther: "fields"
  };

  const requestOptions = {/*GET, url, api_key, etc. */},

// here is where I'm trying to handle this case

try{
  const resolve = await request(requestOptions);
  
  if(resolve) { 

      const newTransaction = new TransactionItem(myUpdatedTransaction) 
      
      await newTransaction.save();

      res.status(201).json(newTransaction);

      return;
  }
}catch(err){
    /******** And here where I don't know how to deal with this *******/
    console.log('error ----->');

    if(err) {
      res.status(409).json({ message: 'Check if the ticker is correct.'});
      console.log('409');

      return;
    }

}

};