How to track the content change of the object loaded via ajax?

On the page you have an element into which loaded data from DB with some frequency.
<div id="answers"></div>

$("#answers").everyTime(10000, function() {
 type: "POST", url: "update.php", data: "id="+zid+"",
 complete: function(data){

How you can track changes in the content of an element inside <div id="answers"></div>?
For example if you change <div id="counter">8</div> to <div id="counter">9</div> display an alert with some text.

PS.: tried here so:
$('#counter').on('DOMSubtreeModified', function(){
 console.log('Content changed');

only responds when I change the value when updating is not working.

Now I read about MutationObserver, but saddened by the lack of support in IE below 11.
July 8th 19 at 12:09
1 answer
July 8th 19 at 12:11
And that prevents the trigger to hang up in complete ?
or call the desired function within that section complete?

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