//this was actually very hard challenge, because i could not figure out how to iterate in the loop

function chunkArrayInGroups(arr, size) {
  var newarr=[];
  //here i set the loop to iterate by arr.length, and i to be incremented by size, because we need to iterate by size.

      for (var i=0; i<arr.length; i+=size){
        //then i push the iteration values inside a new array.
      newarr.push(arr.slice(i,i+size));
      }
console.log(newarr);
}

chunkArrayInGroups([0, 1, 2, 3, 4, 5,6,7,8], 4);