var numbers = [4, 2, 5, 1, 3];
    numbers.sort(function(a, b) {
      return a - b;
    });
    console.log(numbers); // [1, 2, 3, 4, 5]

// for (...) {
    var a = numbers[i];
    var b = numbers[i + 1];
// }

function(a, b) {
    return -123;
}