Issue with "Cross-Origin Resource Sharing (CORS)": (short summary here please)

[johnye2e]

MDN URL: https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS

What information was incorrect, unhelpful, or incomplete?

No event listeners are registered on any XMLHttpRequest.upload object used in the request; these are accessed using the XMLHttpRequest.upload property.

Specific section or headline?

https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS#simple_requests

What did you expect to see?

Perhaps:

No event listeners are registered on any XMLHttpRequest object used in the request; these are accessed using the XMLHttpRequest.upload property.

Did you test this? If so, how?

MDN Content page report details

• Folder: en-us/web/http/cors
• MDN URL: https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS
• GitHub URL: https://github.com/mdn/content/blob/main/files/en-us/web/http/cors/index.html
• Last commit: f89d77d
• Document last modified: 2021-03-07T23:18:07.000Z

[sideshowbarker]

Thanks for reporting this. The object where the event listeners get registered is actually the XMLHttpRequestUpload object, and what’s sort of inherently confusing about this is that given an XMLHttpRequest instance xhr, accessing the xhr.upload property is how you get an XMLHttpRequestUpload object. But basically the only purpose of getting an XMLHttpRequestUpload object is to attach event listeners to it.

But you’re correct that “XMLHttpRequest.upload” isn’t strictly an object; instead, accessing the .upload property from an XMLHttpRequest instance returns an XMLHttpRequestUpload object — and then attaching event listeners to that XMLHttpRequestUpload object is what will trigger a preflight.

So in #3138 I’ve tried to revise the language to make it more clear what we’re talking about.