Sorting

sort.js

var shortArr = [1, 2, 3, 5, 4, 8, 7, 6];

var longArr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 40, 39, 38, 37, 36, 35, 34, 33, 32, 31, 30, 29, 22, 24, 23, 28, 27, 26, 25, 24, 22];

function reSortArray(arr) {
  var limit = 20;

  if (arr.length < limit) {
    return arr.sort();
  } else {
    var originalPart = arr.slice(0, arr.length - (arr.length - limit) );
    var endPart = arr.slice( 0 - limit - 1).sort();
  }
  return originalPart.concat(endPart);
}

console.time('short');
console.log(reSortArray(shortArr));
console.timeEnd('short')

console.time('long');
console.log(reSortArray(longArr));
console.timeEnd('long');

console.time('native')
console.log(longArr.sort(function(a, b) {
  return parseFloat(a) - parseFloat(b);
}));
console.timeEnd('native');