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Re: [whatwg] MutationObserver Spec for AddedNodes Timing & network requests

From: Olli Pettay <Olli.Pettay@helsinki.fi>
Date: Mon, 21 Jul 2014 16:26:38 +0300
Message-ID: <53CD150E.8000608@helsinki.fi>
To: whatwg@whatwg.org
On 07/21/2014 12:21 AM, milakam wrote:
>
> Hi everyone,
>
> A BeforeLoad replacement was never discussed as a target use case for
> MutationObservers, therefore this message.
>
> I'm currently creating a JS cross-browser user script and noticed that
> only Chromium notifies the MutationObserver for an AddedNode before a
> network request is sent (IE and FF don't and won't do anything with the
> changes).
>
> I found the following chromium discussion
> https://code.google.com/p/chromium/issues/detail?id=333318 which states
> the MO as a replacement for BeforeLoad.

MutationObserver shouldn't be used as a replacement for any load related stuff.
MutationObserver is about mutations in DOM tree.



  I think this is great solution
> and it would be fantastic if it can be standardized.
>
No. It would disable several performance optimizations related to page loads.



-Olli



> My own usecase / testcase I created:
> <script type="text/javascript">
> MutationObserver = window.MutationObserver;
> var observer = new MutationObserver(function(mutations) {
>    mutations.forEach(function(mutation) {
>    	var addedNodes = mutation.addedNodes;
> 	for (var i = 0; i < addedNodes.length; i++) {
> 		if (addedNodes[i].nodeName == 'SCRIPT') {
> 			addedNodes[i].src = 'good.js';
> 		}
> 	}
> 	
>    });
> });
> observer.observe(document, {childList: true, subtree: true});
> </script>
> <script type="text/javascript" src="evil.js"></script>
>
> In chrome this works out of the box and "good.js" is called directly
> (without sending any network requests beforehand, if it would be stored
> externally). In FF only "evil.js" is called. The source is updated
> within DOM afterwards, but there's no network request or parsing of the
> updated script (apart from the DOM change it has no effect).
> In FF it's currently only possible with an internal extension like (e.g.
> usecase
> http://stackoverflow.com/questions/5330048/event-before-load-event-for-firefox-extension):
> Components.classes["@mozilla.org/observer-service;1"]
>    .getService(Components.interfaces.nsIObserverService)
>    .addObserver({
>      observe: function(aSubject, aTopic, aData) {
>        if ("http-on-modify-request" == aTopic) {
>          var url = aSubject
>            .QueryInterface(Components.interfaces.nsIHttpChannel)
>            .originalURI.spec;
>          if (url && url.match('facebook')) {
>            aSubject.cancel(Components.results.NS_BINDING_SUCCEEDED);
>          }
>      }
>    }
> }, "http-on-modify-request", false);
>
>   I didn't test it in in Konqueror.
>
> Greetz
> MM
>
>
Received on Monday, 21 July 2014 13:27:09 UTC

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