Structured Clone Algorithm doesn't support FormData object

[tevko]

ISSUE: When working with web-workers, it may be necessary to pass a FormData object to the worker via the postMessage method. Unfortunately, the Structured Clone Algorithm (used by the postMessage method to serialize the data being transferred) does not support FormData objects

Expected: postMessage method serializes FormData object and sends to worker

Actual: DATA_CLONE_ERR exception thrown on postMessage call

[foolip]

Legacy bug: https://www.w3.org/Bugs/Public/show_bug.cgi?id=21652

@annevk

[annevk]

@tevko we could do this I suppose (and it would be useful to define the specifics of fetch() and XMLHttpRequest). However, you can emulate this today through iteration and structured cloning the contents of what gets iterated. Is that not sufficient for your use case or is it just cumbersome?

[tevko]

@annevk that would be perfect, but I haven't been able to find anything that explains how I would successfully do that. Is there a resource anyone can point me to?

[annevk]

This works for me in Firefox (and should work per the specification, see https://xhr.spec.whatwg.org/#formdata):

 let fd = new FormData()
 fd.append("x", "y")
 fd.append("y", new Blob())
 for(let keyValue of fd)
   console.log(keyValue)

[annevk]

This is now whatwg/xhr#55.