Chunky Monkey i dont understand commented code

Tell us what’s happening:

Your code so far

function chunkArrayInGroups(arr, size) {

  var temp = [];
  var result = [];

  for(var i = 0; i < arr.length; i++) {
    if (i % size !== size - 1)// i dont understand this line of code please someone explain me
      temp.push(arr[i]); //temp ab
    else {
      temp.push(arr[i]);//tempa a
      temp = [];//

  if (temp.length !== 0)
     return result;

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

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Link to the challenge:

The line checks if the remaider of the current index of arr divided by size is NOT equal to size - 1. If this evaluates to true for the current index of arr, then it will push the current element of arr into the temp array.