function chunkArrayInGroups(arr, size) {
  var smallArr = [];
  var bigArr = [];
  for(var i=0; i<size; i++){
    for(var j=0; j<(arr.length/size); j++){
      smallArr.push(arr[j]);
    }
    bigArr.push(smallArr);
    smallArr = []
    console.log(smallArr);
  }
  return arr;
}

chunkArrayInGroups(["a", "b", "c", "d","a1", "b1", "c1", "d1"], 2);