var list = document.querySelector('.sort-list');
var sortElem = list.getElementsByTagName('li');
var nEntryArray = Array.prototype.slice.call(sortElem, 0);

nEntryArray.sort(function(a, b) {
  return a.firstChild.nodeValue - b.firstChild.nodeValue
})

while (list.lastChild) {
  list.removeChild(list.lastChild);
}

var sortList = document.createDocumentFragment();
for (i = 0, l = nEntryArray.length; i < l; i++) {
  sortList.appendChild(nEntryArray[i]);
}
list.appendChild(sortList);

<ul class="sort-list">
<li class="l1">31</li>
<li class="l2">11</li>
<li class="l3">16</li>
</ul>