How does this if-else statement inside a function work?

I've been completing challenges on FreeCodeCamp and stumbled upon this solution for an algorithm. Can't comprehend how the if else statement works here.

function chunkArrayInGroups(arr, size) {

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

      for (var a = 0; a < arr.length; a++) {
        if (a % size !== size - 1)
          temp.push(arr[a]);
        else {
          temp.push(arr[a]);
          result.push(temp);
          temp = [];
        }
      }

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

Why is temp = [] at the end of the else block?