I was trying to write a polyfill for array sort in javascript. But It turns out that the comparator doesn’t cause any effect on the polyfill. Any idea how to make it work?

Please find my code below:

const arrA = [2,3,4,1,2,3,1,5,6,8,5,9,3];

const newArr = [...new Set(arrA)];

Array.prototype.myNewSort = function(compareFn) {
    return mergeSort(this);
  
    function mergeSort(arr) {
      if(arr.length <= 1) return arr;
    
      const mid = Math.floor(arr.length / 2);
      const leftArr = arr.slice(0, mid);
      const rightArr = arr.slice(mid);
    
      return merge(mergeSort(leftArr), mergeSort(rightArr));
    }
  
    function merge(left, right) {
      let newArr = [];
    
      while(left.length > 0 && right.length > 0) {
          let newCompareFn = compareFn ? compareFn = (l, r) => l < r : newCompareFn;
      newCompareFn = (left, right) => left > right;
        if(newCompareFn(left[0], right[0])) {
         newArr.push(left.shift());
        } else {
         newArr.push(right.shift())
        }
      }
    
      return [...newArr, ...left, ...right];
    }
  
    function composeCompareFn(compareResult) {
      if(Math.sign(compareResult) === -1) return false;
      if(Math.sign(compareResult) === 1) return true;
      if(compareResult === 0) return false;
    }
}

const sortedArr = newArr.myNewSort((a, b) => a - b);
console.log("sortedArr", sortedArr);