function chunkArrayInGroups(arr, size) {

  var arr2=[];
  var j=0, i=0, numOfGroups=0;
  if(arr.length%size===0)
    numOfGroups=arr.length/size;
  else numOfGroups=arr.length/size+1;
  while((i<numOfGroups)&&(j<arr.length))
    {
      if(j%size===0)
          i++;
      arr2[i].push=(arr[j]);
      j++;
    }
return arr2;
}

chunkArrayInGroups(["a", "b", "c", "d"], 2);