FormData.constructor fails when passed HTMLFormElement in Firefox

[rnicholus]

I ran a very simple test in Firefox 30 OSX: I attempted to pass an HTMLFormElement into a FormData constructor. In the absence of platform.js, the attempt succeeds. As soon as I import platform.js, it fails.

Please see this fiddle for a one-line demo of the issue. When run in Firefox as is, with the console open, you'll see the error. If you remove the platform.js import, it executes without error.

Is Polymer either messing with the FormData constructor, or perhaps HTMLFormElement?

[arv]

We are messing with HTMLFormElement.

A temporary work around is to use

ShadowDOMPolyfill.unwrapIfNeeded

[rnicholus]

Where does ShadowDOMPolyfill live? It doesn't seem to exist in the global namespace when I simply import platform.js 0.3.3.

[arv]

@sjmiles

Which browser? I think it only gets added if needed so it will not be there for Chrome (or future versions of Firefox).

If my assumption is correct you can do something like the following to make it always work.

var unwrapIfNeeded = function(x) {
  return x;
}
if (typeof ShadowDOMPolyfill !== 'undefined') {
  unwrapIfNeeded = ShadowDOMPolyfill.unwrapIfNeeded;
}

[rnicholus]

Ah, I didn't check in Firefox and temporarily forgot that Chrome is the only browser that doesn't need to be shimmed here.

Yes, that does seem to work. I'm extending a form element in a custom element I'm developing, and the following condensed version seems to work (where this is the form I'm extending):

var form = window.ShadowDOMPolyfill ? ShadowDOMPolyfill.unwrapIfNeeded(this) : this;
var formData = new FormData(form);

Thanks for your help on this.

[sjmiles]

When using Polymer, you can always use [window.]unwrap in these situations.

var formData = new FormData(unwrap(this));

[rnicholus]

That makes it much simpler, thanks. Will the recently committed fix be part of 0.3.4?