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
      result.push(temp);// 
      temp = [];//
    }
  }

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


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
















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Link to the challenge:
https://www.freecodecamp.org/challenges/chunky-monkey