16392 2012-03-15 22:03:38 +0000 MutationObserver invocation order should be fixed at the beginning of each loop 2012-03-20 10:50:43 +0000 1 1 1 Unclassified WebAppsWG DOM unspecified All All RESOLVED FIXED P2 normal --- 1 adamk annevk bugs mike www-dom public-webapps-bugzilla oldest_to_newest 65632 0 adamk 2012-03-15 22:03:38 +0000 From www-dom: http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#concept-mo-invokedescribes an algorithm for delivering MutationRecords to MutationObservers. In particular, it describes an order of delivery, and I wonder if tweaking it a little bit would make it simpler to implement. Note that I don't think the particular order is of much importance: it's just important that there is a well-defined order. In particular, there are two cases I'm worried about: 1. Assume observers A, B, and C (created in the order A, B, C). Say that at the beginning of the algorithm, only A and C have non-empty queues. But during A's callback, it mutates DOM that causes a record to be added to B's queue. 2. Assume an observer A with a non-empty queue. During its callback, it creates a new observer B, starts B observing, and mutates DOM that adds a record to both A's and B's queue. By the spec, case (1) would result in the delivery order A-B-C. And (2) would be A-B-A. In the WebKit implementation, though, only the "active" observers (those with records in their queues) are kept in a list (this makes it fast in the common case that there's no delivery necessary). This makes our algorithm more like this: I. Make a copy of the existing "active" list, clear the list, and then iterate over the copy. II. When that iteration is complete, the active list is checked again; if it's non-empty, go back to step I. When applied to the cases above, (1) results in the order A-C-B (B doesn't get notified until the next time around the loop), and (2) results in A-A-B (again, the newly-added observer doesn't get notified until the second time through the loop). ... I've implemented the aforementioned algorithm in WebKit. Per the thread, http://lists.w3.org/Archives/Public/www-dom/2012JanMar/0145.html, it sounds like Olli is fine with that algorithm too (CCing him just in case) 65811 1 annevk 2012-03-20 10:50:43 +0000 https://bitbucket.org/ms2ger/dom-core/changeset/1c5fe3fae8b4