let list = [1,2,3,4,5,6,7,8];
let new_list =[];
let single_list = [];
list=list.reverse()
while(list.length){
single_list.push(list.pop());
if(single_list.length==3){
new_list.push(single_list);
single_list =[];
}
}
if(single_list.length>0){
new_list.push(single_list);
}
console.log(new_list);