//Algorithm of mergeSort which divides the array and conquers
function mergeSort(array) {
  if(array.length<2){
    return array;
  }
  var middleIndex=Math.floor(array.length/2);
  var firstHalf=array.slice(0,middleIndex);
  var secondHalf=array.slice(middleIndex);
  return merge(mergeSort(firstHalf),mergeSort(secondHalf));
}

//Algorithm to merge arrays
function merge(array1, array2) {

  var result = [];
  while (array1.length && array2.length) {
    minElem = 0;
    if (array1[0] < array2[0]) {
      minElem = array1.shift();
    } else {
      minElem = array2.shift();
    }
    result.push(minElem);
  }
  if (array1.length) result = result.concat(array1);
  else result = result.concat(array2);
  return result;
}

mergeSort([1, 3, 2, 8, 4]);