Bug: FormData - Failed to execute 'append' on 'FormData': parameter 2 is not of type 'Blob'

[todor-a]

I'm having issues migrating away from jsdom to jest-fixed-jsdom in order to be able to use msw (I know that migrating away from jsdom altogether is best but this is not feasible at this point).

For this method:

export const uploadDocument = (file: File) => {
    const data = new FormData();
  
    data.append("file", file, file.name);
  };

I get this error:

TypeError: Failed to execute 'append' on 'FormData': parameter 2 is not of type 'Blob'

      2 |     const data = new FormData();
      3 |   
    > 4 |     data.append("file", file, file.name);
        |          ^
      5 |   };
      6 |   

I've setup a reproduction here and would love some help.

[rowan-lovejoy]

Having a very similar issue after upgrading to the Jest 30, which bumps JSDOM to ^22.0.0 (our package-lock has 26.1.0 in it). When I call this method in one of our tests:

const ... = await window.navigator.clipboard.readText();

It fails with this error output:

TypeError: Failed to execute 'readAsText' on 'FileReader': parameter 1 is not of type 'Blob'.                                                                         
      ...                                                                                                                                                            
    > 638 |         const ... = await window.navigator.clipboard.readText();

(Have redacted variable names and error output to hide other, proprietary code. All it showed was the previous function call.)

I was able to fix error this by commenting out the Blob global restoration in jest-fixed-jsdom:

// node_modules/jest-fixed-jsdom/index.js
class FixedJSDOMEnvironment extends JSDOMEnvironment {
  constructor(...args) {
    super(...args)
    ...
    
    // this.global.Blob = Blob
    this.global.Headers = Headers
    ...
  }
}

We're using MSW in this project (2.10.2), and it seems to still work correctly after commenting out the Blob global restoration. Perhaps this restoration is longer necessary with newer JSDOM versions?