[Bug 27320] New: Need some clarification around MutationObserver stuff.

https://www.w3.org/Bugs/Public/show_bug.cgi?id=27320

            Bug ID: 27320
           Summary: Need some clarification around MutationObserver stuff.
           Product: WebAppsWG
           Version: unspecified
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DOM
          Assignee: annevk@annevk.nl
          Reporter: crimsteam@gmail.com
        QA Contact: public-webapps-bugzilla@w3.org
                CC: mike@w3.org, www-dom@w3.org

I tried analyze dependencies across all algorithms and other prose for
MutationObserver oposite to how browsers works, but every time something is
wrong. Here are some inaccuracies:

=== 

callback MutationCallback = void (sequence<MutationRecord> mutations,
MutationObserver observer);

In practice mutations and observer are optional (Firefox/Chrome/IE), so maybe
add "optional" to IDL? And maybe cover this somehow in prose (step 3.4 in
"notify mutation observers").

<script>
    var new_MO = new MutationObserver(function(){});
    alert(new_MO); // create without any problem
</script>

===

Next is more complicated, but I'm not sure whether it is browsers problem or
DOM. This affects mainly to "notify mutation observers" alghoritm and proper
support takeRecords() method. Important thing is that if we operete on orginal
or copy of something (like list or other object).

Look this:
2. Let notify list be a copy of unit of related similar-origin browsing
contexts's list of MutationObserver objects. 

Per spec. callback get only copy of MO (as second argument) but all browsers
operate on original.

<script>

    var new_MO = new MutationObserver(function(records, observer){

        alert(new_MO === observer);
        alert(new_MO === this);
        alert(this === observer);

    });

    var new_P = document.createElement("P");
    new_MO.observe(new_P, {attributes: true});

    new_P.id = "setID";

</script>

Above is important for takeRecords() method because we can use this method for
original (new_MO in our example) and for copy (observer in our example as
second argument for callback or "this" value) directly in callback.
takeRecords() method should clear "record queue", but if we have different
object we have different "record queue" too.

<script>

    var new_MO = new MutationObserver(function(records, observer){

        // All browsers trate new_MO and observer as the same object (instance)
and clear its record queue before invoke callback
        // its correct per step 3.2, but in generaly not per step 2. (algo
"notify mutation observers") because its operate on copy

        var takeFrom_MO = new_MO.takeRecords().length; //  record queue is
empty
        var takeFrom_observer = observer.takeRecords().length; //  record queue
is empty

        document.documentElement.innerHTML += "new_MO.takeRecords().length: " +
takeFrom_MO
            + "<br>" + "observer.takeRecords().length: " + takeFrom_observer

            // This was only copy so we still get 1
            + "<br>" + "records.length: " + records.length
    });

    var new_P = document.createElement("P");
    new_MO.observe(new_P, {attributes: true});

    new_P.id = "setID";

</script>

What do you think?

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Received on Thursday, 13 November 2014 21:03:47 UTC