js string sorting

string-sorting.js

var testString =  "Partner World Dog Cat Xyelephone New. shorts apple summer a tiny"

function sortDescending(a, b){
  if (a > b) return -1
  if (a < b) return 1
  else return 0
}

function sortArrayAndStringify(array, sortComparator){
  var o = "";
  array.sort(sortComparator)
  array.forEach(function(val){ o += val + " " })
  return o // return a sorted string
}

function splitLowerCaseAndSort(string){
  var arr = string.split(" "),
      newArr = [];
  for (var i = 0; i <= arr.length - 1; i++){
    var value = arr[i]
    if (value[0] == value[0].toLowerCase()){
      newArr.push(value)
    }
  }
  return sortArrayAndStringify(newArr)
}


function splitUpperCaseAndSort(string){
  var arr = string.split(" "),
      newArr = [];
  for (var i = 0; i <= arr.length - 1; i++){
    var value = arr[i]
    if (value[0] == value[0].toUpperCase()){
      newArr.push(value)
    }
  }
  return sortArrayAndStringify(newArr, sortDescending)
}


function runTest(string){
  var desiredString = [splitLowerCaseAndSort(string), splitUpperCaseAndSort(string)].join("").trim()
  return desiredString.replace(/\./g,' ')   // replace period in string
}

runTest(testString)