Sorting algorithm that only works for positive numbers. Is it efficient? I doubt it.

arraysort.js

let arrayToSort = [];
for (let i = 1000; i--;) arrayToSort.push(Math.floor(Math.random() * 1000)); // add 1000 random integers between 0-999

function arraySort(arrayToSort) {
  let sortedArray = [],
      array = [];
  for (let i = arrayToSort.length; i--;) {
    if (array[arrayToSort[i]]) array[arrayToSort[i]]++;
    else array[arrayToSort[i]] = 1;
  }
  for (let i = 0; i < array.length; i++) {
    if (array[i]) for (let j = 0; j < array[i]; j++) {
      sortedArray.push(i);
    }
  }
  return sortedArray;
}

/* this sorts your array AND removes its duplicates. how nice? */
function arraySortAndRemoveDuplicates(arrayToSort) {
  let sortedArray = [],
      array = [];
  for (let i = arrayToSort.length; i--;) array[arrayToSort[i]] = 1;
  for (let i = 0; i < array.length; i++) if (array[i]) sortedArray.push(i);
  return sortedArray;
}

console.log(arraySort(arrayToSort), arraySortAndRemoveDuplicates(arrayToSort));