AbortController is undefined in IE11

[yugandhar02]

Describe the bug

Although signalr has ponyfill for AbortController, its not being used in FetchHttpClient.
This leads to error in IE11 where AbortController is not supported

To Reproduce

use fetch polyfill for IE11.

Exceptions (if any)

[BrennanConroy]

We don't support IE11 and recommend users switch to Edge.

Does adding an AbortController polyfill alongside the fetch polyfill fix the issue for you? If so, that's the recommended approach.

If you're interested in contributing a simple fix for IE11 we would consider merging it.

[yugandhar02]

@BrennanConroy Its not just about IE11.
It will break in older browser which doesn't have abortController support.
I see that signalr already has ponyfill for abortController which is being used in other places e.g. longPollingTransport.
Can that be used ?

[JunTaoLuo]

Let's doc this.

Thanks for contacting us.
We're moving this issue to the Next sprint planning milestone for future evaluation / consideration. We will evaluate the request when we are planning the work for the next milestone. To learn more about what to expect next and how this issue will be handled you can read more about our triage process here.

[pleunv]

Also kind of surprised this suddenly made it in the last release. Would it be possible to use the ponyfill for now, as @yugandhar02 suggested? Alternatively using a polyfill like https://github.com/mo/abortcontroller-polyfill in userland works as well, but a little bit unnecessary if SignalR already has a ponyfill in place.

I understand the desire to drop IE11, but a change like this on a major .NET Core upgrade has pretty severe consequences, especially if they're not well documented (and not just here, but on the general .NET Core v5 documentation as well). Spending a few days updating your codebase to v5 to then find out you suddenly lost IE11 support is kind of... troublesome.

[pleunv]

I'd also like to add that the version support listed here is rather unsatisfactory. You can't realistically expect companies to depend on a JS library if all you officially support is the latest version across all browsers. 7-10% of our (corporate) user base is on IE11, a larger percentage of that is still on a non-chromium Edge. This means that a critical piece of the .NET Core stack (for us at least) could break at any moment, and impact a significant percentage of our users.

[bradygaster]

As @BrennanConroy stated, we don't support IE11 and recommend customers move to Edge. Does the workaround @BrennanConroy suggested result in the app working in IE11? If so, is your concern that, with that fix it will work in IE11 but not in older-than-IE11 browsers?