event.composedPath()[0] can be very slow: add event.composedTarget?

[justinfagnani]

We have a report that event.composedPath() can be slow enough to drastically slow down an initial render that uses it heavily (~29% percent of initial render time).

This use case, and a few others I've seen, only needs the composed target, not the full path, (ie event.composedPath()[0]). Could we add Event.prototype.composedTarget so the full path doesn't need to be materialized?

[EisenbergEffect]

+1 to this. I hadn't seen the perf issue, but this is a very common pattern with composedPath() and it would make things much easier to teach and understand if a dedicated composedTarget property were available.

[dbatiste]

+1. We use event.composedPath()[0] a whole bunch.