NodeJs express error middleware parsing

Question

I am trying to write a middleware to handle errors. But I cannot figure out how to send the correct format to my frontend. Below I am going to list all of my attempts in hopes of helping you help me.

Attempt 1

app.use(function(err, req, res, next) {
    const formatted = err;
    res.send(formatted)
});

result in postman

{ "code": 422 }

Attempt 2

app.use(function(err, req, res, next) {
    const formatted = `${err}`;
    res.send(formatted)
});

result (postman)

Error: Request returned error code: 422 and body: {"status":422,"title":"The display name: build_id has already been used on this product.","type":"https://developer.bigcommerce.com/api#api-status-codes","errors":{"display_name":"The display name: build_id has already been used on this product."}}

That is the data i want but i need it in json

Question Why is there more data revealed after string interpolation? How can i format it to json?

Possible duplicate of [Proper way to set response status and JSON content in a REST API made with nodejs and express](https://stackoverflow.com/questions/26066785/proper-way-to-set-response-status-and-json-content-in-a-rest-api-made-with-nodej) — Robert Moskal, Aug 15 '18 at 18:28
The error your `console.log()` is not JSON it is a text. I think your error is related to **bigcommerce** as it returned in the message — Hello World, Aug 15 '18 at 19:15
why is it text? I know the API res (when i try in postman) returns json... turns it to text somewhere — Omar, Aug 15 '18 at 19:17
`Error: Request returned error code: 422 and body: {"status":422,"title":"The display name: build_id has already been used on this product.","type":"https://developer.bigcommerce.com/api#api-status-codes","errors":{"display_name":"The display name: build_id has already been used on this product."}}` <-- This is actually a text/string. I don't know why !! On my understanding this is related to any of your external library which is causing it. I would suggest you to focus on the problem you are getting in `console` which is `The display name: build_id has already been used on this product.` — Hello World, Aug 15 '18 at 19:25
... and Then focus on the middleware issue. The response `{ "code": 422 }` is all we have. Problem is not in the middleware. — Hello World, Aug 15 '18 at 19:28
i dont want to fix the error. I want to send the error to my frontend — Omar, Aug 15 '18 at 19:30

rickjerrity · Answer 1 · 2018-08-15T18:34:15.710

0

You're probably looking for res.json(err) if I had to guess?

https://expressjs.com/en/api.html#res.json

EDIT: Full example:

app.use(function(err, req, res, next) {
    if (err) res.json(err)
});

edited Aug 15 '18 at 18:34

answered Aug 15 '18 at 18:26

rickjerrity

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That gives me json but not the full message... see `attempt 5` (just added) – Omar Aug 15 '18 at 18:30
You're still doing it wrong. I'll update my answer to be more clear. – rickjerrity Aug 15 '18 at 18:33
That is not retuning the full message. `>{"code": 422 }`... Look at the difference between attempt one and two. That is the problem i need to figure out – Omar Aug 15 '18 at 18:38

Hello World · Answer 2 · 2018-08-15T19:34:25.313

-1

You can do it in this way

app.use(function(err, req, res, next) {
    if (err) {
        res.json({
            status: "error",
            error: `${err}` // <-- edited
        });
    } else {
        next();
    }
});

edited Aug 15 '18 at 19:34

answered Aug 15 '18 at 18:32

Hello World

2,673
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If you look at attempt 1 there is only `{ "code": 422 }` until attempt 2 where i did string interpolation. That is the same problem im having when i tried this. Only the code returns but not the message. – Omar Aug 15 '18 at 18:36
@Omar can you explain it a bit more about the context like what request you are sending etc, this will help us find the problem. – Hello World Aug 15 '18 at 18:40
Did you tried sending the request via other platform or any browser?? – Hello World Aug 15 '18 at 18:42

NodeJs express error middleware parsing

Attempt 1

Attempt 2

Question Why is there more data revealed after string interpolation? How can i format it to json?

2 Answers2