var itemSet=new Set(["JavaScript","HTML","CSS"]);
var list=document.getElementById("test-list");
var itemList=list.children;
var delItemArr=[];
for(var i=0;i<itemList.length;i++){
   if(!itemSet.has(itemList[i].innerHTML)){
     delItemArr.push(itemList[i]);
   }
}
delItemArr.forEach(function(item){
  list.removeChild(item);
});