determine if an array is sortable with one swap

swap.js

// test arrays
var x = [1, 2, 3];
var y = [1, 3, 2];
var z = [3, 2, 1];

// global swap counter
var swaps = 0;

// custom sort function that counts swaps
function swapcount(a, b){
 if (a < b) {
   return -1;
  } else if (a > b) {
    swaps++;
    return 1;
  }

  return 0;
}

// shallow compare two arrays
function compareAr(a, b) {
  if (a.length !== b.length) return false;

  for (var i = 0; i < a.length; i++) {
    if (a[i] !== b[i]) return false;
  }

  return true;
}

// test function
function solution(a) {
  var sorted = a.slice().sort();

   // true when already sorted
  if (compareAr(a, sorted)) return true;

  // count swaps
  swaps = 0
  a.sort(swapcount);

  // false when more than one swap is needed
  if (swaps > 1) {
    return false;
  }

  // true when sorated with one swap
  return true;
}

[x, y, z].forEach(ar => console.log(solution(ar)));