Can we add a 'done' event?

[daniel-bryant]

Thanks in advance! My usage looks like this.

es = new EventSource(url, {
  debug: debug,
  headers: headers,
  pollingInterval: 0, // Set pollingInterval to 0 to disable reconnections
})

I set pollingInterval to 0 as suggested in the README because otherwise it would reconnect and I don't need reconnections. However, I do want to know when the request "finishes".

The server closing does not trigger a close event, which seems to be by design. But I noticed [EventSource][onreadystatechange][DONE] Operation done. in the debug logs. That is exactly what I need to know in my code, but there's no event!

I forked the source locally, added the event, and things work perfectly 👌. The actual change is only a handful of lines, so I can easily make a PR. Just wanted to get a 👍 first.

[wojciechkrol]

Feel free to open PR