One mystery solved, *so* many more revealed: https://twitter.com/slightlylate/status/1184958694523453440 …pic.twitter.com/qHj0uyb9lh
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Ah, OK, I see what you're saying about `.response` + `responseType`. Would have to dig into code to see if it's actually async in our impl: https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/response … But it doesn't look like it? https://cs.chromium.org/chromium/src/third_party/blink/renderer/core/xmlhttprequest/xml_http_request.cc?rcl=cf4a16f050bfd5cc5489cb897ae1c0756f49309a&l=1922 … The value of .response is synchronously available, I guess?
It's synchronously available, but set only upon successful completion of the request, so browser is free to perform parsing on another thread and/or in streaming fashion, and then fire onload and other events when it's all done.
(I'm not sure either which if any implementations do this without looking at code though, just stating that API-wise both XHR2 and Fetch allow this.)
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