TypeScript - Unable to access FormidableError on formidable.errors

[FredTheNoob]

Support plan

• Which support plan is this issue covered by? (Community, Sponsor, Enterprise): Community
• Currently blocking your project/work? (yes/no): no
• Affecting a production system? (yes/no): no

Context

• Node.js version: 18.18.2
• Release Line of Formidable (Legacy, Current, Next): Current
• Formidable exact version: ^3.4.5
• Environment (node, browser, native, OS): node
• Used with (popular names of modules): express, typescript, es6 imports

What are you trying to achieve or the steps to reproduce?

I'd like to access the FormidableError object when I'm throwing an error, this is my use case:

router.post("/user/upload", validateAuthToken, async (req, res, next) => {
    const form = formidable({
        maxFiles: 1, 
        keepExtensions: true, 
        maxFileSize: MAX_FILE_SIZE, 
        allowEmptyFiles: false,
    });

    form.parse(req, async (err, fields, files) => {
        if (err) {
            if (err instanceof formidable.errors.FormidableError) {
                return res.status(err.httpCode ? err.httpCode : 400).send(err.message);
            }
        }
    })
});

In postman I'm passing multipart formdata, where I purposely input a file above the MAX_FILE_SIZE, the error is thrown properly, but I just seem unable to get the FormidableError object.

What was the result you got?

TypeError: Cannot read properties of undefined (reading 'FormidableError')

What result did you expect?

That the above use case works

[tunnckoCore]

That's because errors export named variables with "error codes", not directly the error class.

That's a good point, we'll fix it. I think you can access the class on errors.default.

[GrosSacASac]

Where did you see that way of using this variable ?

[FredTheNoob]

Where did you see that way of using this variable ?

Nowhere, in retrospect I don't know if this is even the right way to do it at all 😅

[FredTheNoob]

That's because errors export named variables with "error codes", not directly the error class.

That's a good point, we'll fix it. I think you can access the class on errors.default.

That doesn't seem to work 😔

[GrosSacASac]

import formidable, {errors as FormidableErrors} from 'formidable';

console.log(FormidableErrors.default);

formidable.errors is not the same as FormidableErrors.
The way you import is critical here

https://github.com/node-formidable/formidable/blob/master/src/FormidableError.js

or

As you can see all errors have a httpCode

So you could do the following

if (err.httpCode !== undefined)

[FredTheNoob]

I don't know how to apply that to my example @GrosSacASac.
I've tried this:

import formidable, {errors as FormidableErrors} from 'formidable';

....

form.parse(req, async (err, fields, files) => {
        if (err) {
            if (err instanceof FormidableErrors.FormidableError) {
                if (err.httpCode !== undefined) {
                    return res.status(err.httpCode).send(err.message);
                }
            }
        }
});

But get this error:

file:///root/easyrate/easyrate-backend/js/routes/user.js:283
            if (err instanceof FormidableErrors.FormidableError) {
                    ^

TypeError: Right-hand side of 'instanceof' is not an object
    at file:///root/easyrate/easyrate-backend/js/routes/user.js:283:21
    at zalgoSafe (/root/easyrate/easyrate-backend/node_modules/dezalgo/dezalgo.js:20:10)
    at f (/root/easyrate/easyrate-backend/node_modules/once/once.js:25:25)
    at IncomingForm.<anonymous> (file:///root/easyrate/easyrate-backend/node_modules/formidable/src/Formidable.js:225:7)
    at IncomingForm.emit (node:events:519:28)
    at IncomingForm._error (file:///root/easyrate/easyrate-backend/node_modules/formidable/src/Formidable.js:495:10)
    at Stream.<anonymous> (file:///root/easyrate/easyrate-backend/node_modules/formidable/src/Formidable.js:385:14)
    at Stream.emit (node:events:519:28)
    at MultipartParser.dataPropagation (file:///root/easyrate/easyrate-backend/node_modules/formidable/src/plugins/multipart.js:103:22)
    at MultipartParser.emit (node:events:531:35)

Node.js v21.7.1

import formidable, {errors as FormidableErrors} from 'formidable';

console.log(FormidableErrors.default);

formidable.errors is not the same as FormidableErrors. The way you import is critical here

https://github.com/node-formidable/formidable/blob/master/src/FormidableError.js

or

As you can see all errors have a httpCode

So you could do the following

if (err.httpCode !== undefined)

[GrosSacASac]

if (err instanceof FormidableErrors.default)

[FredTheNoob]

That doesn't work either

I have imported like so:

import formidable, {errors as FormidableErrors} from 'formidable';

[Corpra]

@FredTheNoob

I'm doing this successfully with the following:

import { errors as formidableErrors } from 'formidable';

// ...

if e (instanceof formidableErrors.FormidableError)

But I'm on v2 of formidable, not sure if that matters.

[vircoding]

I'm doing this to verify the error type in v3.5.2

import formidable, { errors as formidableErrors } from 'formidable';

try {
  [fields, files] = await form.parse(event.node.req);
} catch (error) {
  if (error && typeof error === 'object' && 'code' in error) {
    if (error.code === formidableErrors.biggerThanMaxFileSize)
      throw new BadRequestError('File exceeds the maximum allowed size of 5MB');
    }
  throw new UnexpectedError();
}