NodeJs表达错误中间件解析

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?

Answer 1

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)
});

Answer 2

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();
    }
});