[Danxil]

Для IE 11+ и ост. браузеров:

var target = document.querySelector('#some-id');
 
var observer = new MutationObserver(function(mutations) {
  mutations.forEach(function(mutation) {
     // ...
  });    
});

var config = { attributes: true };
 
observer.observe(target, config);

Для IE 9+, FF, Opera

var target = document.querySelector('#some-id');

target.addEventListener("DOMAttrModified", function (ev) {
  // ...
}, false);

Подробнее - https://developer.mozilla.org/en-US/...tationObserver,
https://developer.mozilla.org/en-US/...utation_events