950519 - mutation.oldValue does not hold old value when attribute is removed

Status: RESOLVED WORKSFORME

(Firefox :: Untriaged, defect)

Description

[noitidart]

User Agent: Mozilla/5.0 (Windows NT 5.1; rv:26.0) Gecko/20100101 Firefox/26.0 (Beta/Release)
Build ID: 20131205075310

Steps to reproduce:

I attached a mutation observer to the findbar (xul), when the attribute hidden is added it holds proper oldValue of null. However when hidden attribute is removed, mutation.oldValue does not hold the old value which was true

here is the code to run from scratchpad:

function disconMObs() { //run this to undo the changes
  for (var m=0; m<mObservers.length; m++) {
    if (mObservers[m].win == domWindow) {
        mObservers[m].obs.disconnect()
    }
  }
}

if (!mObservers) {
var mObservers = []; //a new observer per window //holds [{win: window, obs: observer}
var mObserverConfig = { attributes: true };
}

  var browserEnumerator = Services.wm.getEnumerator("navigator:browser");
  while (browserEnumerator.hasMoreElements()) {
    var browserWin = browserEnumerator.getNext();
    var tabbrowser = browserWin.gBrowser;
    var numTabs = tabbrowser.browsers.length;
    var domWindow = browserWin.QueryInterface(Ci.nsIDOMWindow);
    
    for (var index = 0; index < numTabs; index++) {
      //var currentBrowser = tabbrowser.getBrowserAtIndex(index);
      var aTab = tabbrowser.tabContainer.childNodes[index];
      var findbar = aTab._findBar;
      if(!findbar) {
        findbar = tabbrowser.getFindBar(aTab);
      }
      
      var obsForWinFound = false;
      for (var m=0; m<mObservers.length; m++) {
        if (mObservers[m].win == domWindow) {
            mObservers[m].obs.observe(findbar, mObserverConfig);
            obsForWinFound = true;
            break;
        }
      }
      
      if (!obsForWinFound) {
        mObservers.push({
            win: domWindow,
            obs: new domWindow.MutationObserver(function(mutations) {
                     mutations.forEach(function(mutation) {
                        var attributeName = mutation.attributeName;
                        if (attributeName == 'hidden') {
                            var oldValue = mutation.oldValue;
                            alert(attributeName + ' changed to ' + mutation.target.getAttribute('hidden'));
                        }
                     });    
                 })
        });
        mObservers[mObservers.length-1].obs.observe(findbar, mObserverConfig);
      }
      break;
    }
  }




Actual results:

when attribute is removed it woudl show that mutaiton.oldValue holds null


Expected results:

mutation.oldValue should have held true

Comment 1

[noitidart]

wait actually never mind. i dont know what i was doing but yesterday it wouldnt give me the value but today it works as expected.

Comment 2

[:Gijs (he/him)]

(In reply to noitidart from comment #1)
> wait actually never mind. i dont know what i was doing but yesterday it
> wouldnt give me the value but today it works as expected.

OK!