var observeDOM = (function(){
  var MutationObserver = window.MutationObserver || window.WebKitMutationObserver;

  return function( obj, callback ){
    if( !obj || obj.nodeType !== 1 ) return; 

    if( MutationObserver ){
      // define a new observer
      var mutationObserver = new MutationObserver(callback)

      // have the observer observe for changes in children
      mutationObserver.observe( obj, { childList:true, subtree:true })
      return mutationObserver
    }
    
    // browser support fallback
    else if( window.addEventListener ){
      obj.addEventListener('DOMNodeInserted', callback, false)
      obj.addEventListener('DOMNodeRemoved', callback, false)
    }
  }
})()


//------------< DEMO BELOW >----------------

// add item
var itemHTML = "<li><button>list item (click to delete)</button></li>",
    listElm = document.querySelector('ol');

document.querySelector('body > button').onclick = function(e){
  listElm.insertAdjacentHTML("beforeend", itemHTML);
}

// delete item
listElm.onclick = function(e){
  if( e.target.nodeName == "BUTTON" )
    e.target.parentNode.parentNode.removeChild(e.target.parentNode);
}
    
// Observe a specific DOM element:
observeDOM( listElm, function(m){ 
   var addedNodes = [], removedNodes = [];

   m.forEach(record => record.addedNodes.length & addedNodes.push(...record.addedNodes))
   
   m.forEach(record => record.removedNodes.length & removedNodes.push(...record.removedNodes))

  console.clear();
  console.log('Added:', addedNodes, 'Removed:', removedNodes);
});


// Insert 3 DOM nodes at once after 3 seconds
setTimeout(function(){
   listElm.removeChild(listElm.lastElementChild);
   listElm.insertAdjacentHTML("beforeend", Array(4).join(itemHTML));
}, 3000);

<button>Add Item</button>
<ol>
  <li><button>list item (click to delete)</button></li>
  <li><button>list item (click to delete)</button></li>
  <li><button>list item (click to delete)</button></li>
  <li><button>list item (click to delete)</button></li>
  <li><em>&hellip;More will be added after 3 seconds&hellip;</em></li>
</ol>