How to use MutationObserver?

Question

I recently came across this awesome MutationObserver feature which sort of keep tracks of the changes on any dom element. I used the code that was shown on the mozilla developer network, but can't seem to make it run. This is the code I used (link):

   // create an observer instance
var target = document.querySelector('#something');
console.log(target);
var observer = new WebKitMutationObserver(function(mutations) {
    mutations.forEach(function(mutation) {
      console.log("Success");
        //$('#log').text('input text changed: "' + target.text() + '"');
        //console.log(mutation, mutation.type);
    });    
});
observer.observe(target, { attributes: true, childList: true, characterData: true });
//observer.disconnect(); - to stop observing

// test case
setInterval(function(){
    document.querySelector('#something').innerHTML = Math.random();
},1000);

The above code doesn't seems to work. However if I modify the same code with a bit of jQuery, everything seems to work just fine (Demo here). Is there something I'm missing from the docs or I'm just misinterpreting the observer feature.

Answer 1

You need subtree: true

http://jsfiddle.net/6Jajs/1/

The inner text would normally be a child text() element in the DOM. Without the subtree it will only watch the element itself.

There is possible confusion surrounding "characterData" (https://developer.mozilla.org/en-US/docs/Web/API/CharacterData), but it seems that that applies only to nodes that directly contain text. The DOM is structured so that most markup elements contain mixed type which optionally include a child text node (which in turn would implement characterData, but would be a child of the targeted node).