Replace "instanceof" due to DOM realm mixin when Blazor is IFRAME-d

[GStoynev]

When the Blazor page is in an IFRAME in Chrome (or Edge), the Comments (and potentially other HTML elements) in the frame fail the instanceof test because they're instances of frame's parent's Comment.

Replacing instanceof with this prototype check fixes the issue.

Issue is documented here: #55107

Fixes #55107

[GStoynev]

@dotnet-policy-service agree

[javiercn]

This check is incorrect, the right check should be element instanceof element.ownerDocument.defaultView.Comment.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/instanceof#instanceof_and_multiple_realms

[javiercn]

Also, rather than spread this logic all over, we should put it on a helper method isComment to ensure the check is the same across all the callsites.

[GStoynev]

Tested using element instanceof element.ownerDocument.defaultView.Comment. Result is similar to the original Microsoft implementation - the Comment element is NOT detected as such in all cases.

Here is the code and the console output when the error is present:

if (e instanceof Comment) {
  return e.parentNode;
} else if (Object.prototype.toString.call(e) === "[object Comment]") {
  console.warn("---> This *was NOT* detected as a Comment, but *is* one. element instanceof element.ownerDocument.defaultView.Comment is ", e instanceof e.ownerDocument.defaultView.Comment)
}

throw new Error("Not a valid logical element ", e)

When the error occurs, this is what is printed in the console - notice the false:
---> This *was NOT* detected as a Comment, but *is* one. Caller is reaching out for the parent node here. Btw element instanceof element.ownerDocument.defaultView.Comment is false

[GStoynev]

More console output while stopped at a breakpoint during console.warn above:

[javiercn]

@GStoynev why can't we do (element instance of Comment || (window.frameElement && element instanceof window.frameElement.ownerDocument.defaultView.Comment))

Can you put up a repro as a public github repository to make sure we are looking at the same thing? I would expect element.ownerDocument to be the same as window.frameElement.ownerDocument when element is inside the iframe.

[javiercn]

Also, please retarget this PR to main. Changes should go first to main, and then we decide through our process if we backport them to previous versions.

[GStoynev]

Also, please retarget this PR to main. Changes should go first to main, and then we decide through our process if we backport them to previous versions.

Considering proposed alternative by @javiercn doesn't give us what we want, should I proceed with my original idea and issue the PR against main?

[GStoynev]

@javiercn, I'm back from a trip. I think some of our back-and-forth has disappeared - I had posted here the screenshots from (window.frameElement && element instanceof window.frameElement.ownerDocument.defaultView.Comment. Using that construct didn't provide the expected result - its evaluating to the same result as what plain instaneof gives us.

Also, you had mentioned about a minimal reproduction - unfortunately I am unable to provide a minimal reproduction at this time as we're working with a larger closed-source code base.

If an alternative to instanceof is acceptable, why not use what I originally proposed?

This check is incorrect

Could you elaborate why?