Stefan•2mo ago

“TypeError: Illegal constructor” error when using FormData

I'm currently experimenting with the Deno test runner and have set up a simple test. Or at least, I thought I had! When running the test I get the following error:

./tests/async-forms.test.ts (uncaught error)
error: (in promise) TypeError: Illegal constructor
        return new FormData(form, submitter);
               ^
    at Module.illegalConstructor (ext:deno_webidl/00_webidl.js:1158:9)
    at new FormData (ext:deno_fetch/21_formdata.js:93:14)
    at getFormData (file:///home/pepper/Websites/uncluttered/static/get-form-data.ts:8:9)
    at file:///home/pepper/Websites/uncluttered/tests/async-forms.test.ts:24:18
This error was not caught from a test and caused the test runner to fail on the referenced module.
It most likely originated from a dangling promise, event/timeout handler or top-level code.

./tests/async-forms.test.ts (uncaught error)
error: (in promise) TypeError: Illegal constructor
        return new FormData(form, submitter);
               ^
    at Module.illegalConstructor (ext:deno_webidl/00_webidl.js:1158:9)
    at new FormData (ext:deno_fetch/21_formdata.js:93:14)
    at getFormData (file:///home/pepper/Websites/uncluttered/static/get-form-data.ts:8:9)
    at file:///home/pepper/Websites/uncluttered/tests/async-forms.test.ts:24:18
This error was not caught from a test and caused the test runner to fail on the referenced module.
It most likely originated from a dangling promise, event/timeout handler or top-level code.

This is the file in which the error occurs: https://codeberg.org/stefanfrede/uncluttered/src/branch/feature/switch-to-deno-test/static/get-form-data.ts This is the test file: https://codeberg.org/stefanfrede/uncluttered/src/branch/feature/switch-to-deno-test/tests/async-forms.test.ts The idea is to test whether my function returns the correct form values. To be honest, I currently have no idea why this error occurs, so I would be very grateful for any suggestions on how to solve it.

6 Replies

Doctor 🤖•5w ago

I'd guess this happens because it's inside Deno and it doesn't have a real DOM. Try omitting the submitter argument

bartlomieju•5w ago

It's actually the form argument

bartlomieju•5w ago

According to MDN https://developer.mozilla.org/en-US/docs/Web/API/FormData/FormData form should be the DOM element and yeah - Deno doesn't have DOM API support

MDN Web Docs

FormData: FormData() constructor - Web APIs | MDN

The FormData() constructor creates a new FormData object.

bartlomieju•5w ago

@crowlKats any idea how this should work?

crowlKats•5w ago

we dont accept any arguments to the constructor since we dont have the DOM. Since the DOM present in the test file us a userspace package, we cant integrate with it.

StefanOP•4w ago

Thank you for the infos 🙏

“TypeError: Illegal constructor” error when using FormData

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