Merge Sort Implementation

mergesort.js

// following Khan Academy's structure
// https://www.khanacademy.org/computing/computer-science/algorithms/merge-sort/a/overview-of-merge-sort

function mergeSort(array,p,r){
  if(p < r){
    var q = Math.floor((p + r)/2);
    mergeSort(array, p, q);
    mergeSort(array, q+1, r);
    merge(array, p, q, r);
  }
}

var merge = function(array, p, q, r) {
  var lowHalf = [];
  var highHalf = [];

  var k = p;
  var i;
  var j;
  for (i = 0; k <= q; i++, k++) {
    lowHalf[i] = array[k];
  }
  for (j = 0; k <= r; j++, k++) {
    highHalf[j] = array[k];
  }
  k = p;
  i = 0;
  j = 0;

  while (i < lowHalf.length && j < highHalf.length) {
    if (lowHalf[i] < highHalf[j]) {
      array[k] = lowHalf[i];
      i += 1;
    } else {
      array[k] = highHalf[j];
      j += 1;
    }
    k += 1;
  }
  
  while (i < lowHalf.length) {
    array[k] = lowHalf[i];
    k += 1;
    i += 1;
  }
  while (j < highHalf.length) {
    array[k] = highHalf[j];
    k += 1;
    j += 1;
  }
};

var array = [-5, 15, -10, 0, 25, 5, 1, 2];
mergeSort(array, 0, array.length-1);
console.log("Array after sorting: " + array);