Detect script defer support without testing

Question

Is there a reliable way of detecting if a browser supports the <script> attribute "defer" without testing? I'm not interested in creating multiple script blocks both defered and not and seeing which executes first. I'm looking for legitimate feature detection. "defer" in document.createElement("script") returns true just about everywhere, giving a lot of false positives.

Answer 1

Based on Paul Irish's comprehensive research and article on script @defer document in his lazyweb-requests repository, I don't think defer behaves reliably enough to use even if you could feature detect it.