103916 2012-12-03 12:20:32 -0800 MutationObservers should be passed unique MutationRecords 2017-07-18 08:29:22 -0700 1 1 1 Unclassified WebKit WebCore Misc. 528+ (Nightly build) Unspecified Unspecified NEW WebExposed P2 Normal --- 68729 1 adamk webkit-unassigned bedney rafaelw rniwa syoichi oldest_to_newest 781757 0 adamk 2012-12-03 12:20:32 -0800 This is per a change to the DOM spec: see https://www.w3.org/Bugs/Public/show_bug.cgi?id=20131 and https://github.com/whatwg/dom/commit/b5d05659b682b2560af6c24e2e2cdbace82811d3 To minimize the memory impact/mutation-time cost, we could create these unique records only at delivery time (when we're already walking through the list of records to move them from a WTF::Vector to a JS array). Or if we want to get fancy we could build machinery to give each observer its own JS wrapper around a single record. 1059892 1 bedney 2015-01-08 11:43:09 -0800 This bug really caused me a lot of confusion. I have a long-lived MO that observes changes on the #document node (observing both childList and subtree, of course). I wondered why I was seeing a lot of the same Mutation Records over and over again (and this list grows as my app runs). For now, I mark these objects with an expando slot to let me know the record has already been processed, but this should be unnecessary (and it's wildly inefficient to be called with records I've already processed).