Add missing methods for FormData type

[NColey]

Fixes microsoft/TypeScript#14813 by updating the existing append method to better match the Web APIs and adding missing methods. Please let me know if there is anything I should add or change, thanks!

[msftclas]

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[mhegazy]

From the spec: https://xhr.spec.whatwg.org/#formdata the definition should look like:

type FormDataEntryValue = File or string;

interface FormData {
  append(name: string, value: string): void;
  append(name:string, blobValue:Blob, filename?:string):void;
  delete(name: string):void;
  get(name:string):  FormDataEntryValue | null;
  getAll(name: string): FormDataEntryValue[];
  has(name: string): boolean;
  set(name:string, value:string): void;
  set(name: string, blobValue:Blob, filename?: string): void;
};

[Jessidhia]

You can add arbitrary Blob, but you can only get File back? interesting

[NColey]

My apologies @mhegazy , I had been referencing the definitions here: https://developer.mozilla.org/en-US/docs/Web/API/FormData. I just updated the PR to match the appropriate definitions from the spec, thank you for sharing the link with me!

[mhegazy]

Still have a few anys left:

type FormDataEntryValue = File | string;

interface FormData {
  append(name: string, value: string): void;
  append(name:string, blobValue:Blob, filename?:string):void;
  delete(name: string):void;
  get(name:string):  FormDataEntryValue | null;
  getAll(name: string): FormDataEntryValue[];
  has(name: string): boolean;
  set(name:string, value:string): void;
  set(name: string, blobValue:Blob, filename?: string): void;
}

[NColey]

Ah sorry, I have a quick question before I update my PR, if I can't find a FormDataEntryValue interface in the generated file does that make it ok to add it as a type anyway? Or should that be added first?

[Jessidhia]

That is correct, it's just a type so it should not be in the generated code, but it should be available to users to use as a type.

[NColey]

Thanks so much, that makes sense! I just updated the PR with the appropriate types added in.

[Jessidhia]

Ah, looking in the full diff I understand better what you meant.

It seems you need to add FormDataEntryValue to the json file as a typedef (search "typedef" in it to find examples)

[NColey]

@Kovensky Is there another area beyond just as a typedef where it might need to be added? I just updated my PR with the typedef for FormDataEntryValue but the test is failing with the following error Error: The baseline file verifyDefaultLIb_dom.errors.txt has changed. which is both a file that I don't seem to have and also one I suspect I shouldn't touch. I can't seem to figure out what in my changes would have prompted that but I'm guessing there is another area of the code where I would need to add FormDataEntryValue?

[mhegazy]

I think you mean Blob, my guess is this is what is causing the test failure.

[NColey]

You're totally right, thanks so much for catching that. I just fixed it and it seems to be passing now. Thank you!

[mhegazy]

thanks!

[NColey]

Thank you!