On Fri, Jun 29, 2012 at 2:44 AM, Jonas Sicking <[email protected]> wrote:
> All in all I think that as soon as we introduce exceptions to when > MutationObserver callbacks fire we change the API from being a > reliable way to track DOM mutations to a unreliable way where all > callers have to be aware of exceptions and deal with them in other > ways. I.e. it feels like it significantly reduces the value of > MutationObservers. > > And so far I don't see any good arguments made for making that > reduction in value. Did I miss any arguments other then the randomness > argument? > Performance was one concern that's come up in discussing this with Ojan and Rafael. Imagine a MutationObserver attached to the document near the top of the page. Now we need to create basically one MutationRecord per node inserted (because the parser operates in a depth-first sort of order). I'm not at all sure this is a show-stopper (we might be able to introduce some new MutationRecord type that could compactly represent parser-style operation), but it definitely seems worrisome, especially given that one of the common uses for MutationObservers is extensions which might run on many (all?) pages. - Adam
