reorder
HTML
<div class="wrapper">
<div class="abc">a</div>
<div class="abc">b</div>
<div class="abc">c</div>
</div>
JavaScript
var arr = [2,1,0];
var wrapper = document.getElementsByClassName("wrapper");
var items = wrapper[0].children;
var elements = document.createDocumentFragment();
arr.forEach(function(idx) {
elements.appendChild(items[idx].cloneNode(true));
});
wrapper[0].innerHTML = null;
wrapper[0].appendChild(elements);