[shubik22]

This has been my experience as well. At a prior job, we experimented with deferring reporting/tracking functions until the browser was idle, and then firing the remaining tracking events on unload and found that a non-trivial number of events were just dropped (I believe due to this issue).

[littlestymaar]

Funny, because that was almost exactly my use-case as well. I guess sending network requests during the onload event doesn't work well, but maybe for local things it works better, who knows.