Chunk Monkey Challenge

I am struggling with the Chunk Monkey challenge (in the Basic Algorithm Scripting section).
My code is:

function chunkArrayInGroups(arr, size) {
  // Break it up. 
  var newArray = []; 
  var elementArray = [];
  var j;
  for (var i=0; i<arr.length; i++){
    j = i % size; 
    elementArray[j] = arr[i]; 
    if (j==(size-1) || i==(arr.length-1)){
     newArray.push(elementArray);
    } 
  }
  return newArray;
}
chunkArrayInGroups(["a", "b", "c", "d"], 2);

I don’t know what wrong with that but result is [ [“c”,“d”],[“c”, “d”] while the right answer should be [ [“a”,“b”],[“c”,“d”]]. Could anyone help me. Thank you very much!