code: function appendChild(parent, childrens) {
    if (childrens.length === undefined) childrens = [childrens];
    var docFrag = document.createDocumentFragment(); //we used for loop instead of forEach because childrens can be array like object
  
    for (var i = 0, ln = childrens.length; i < ln; i++) {
      docFrag.appendChild(childrens[i]);
    }
  
    parent.appendChild(docFrag);
  }
docs: function to append childrens on a parent