how the sort function works javascript

var ages = [18, 21, 9, 41, 35, 24]
ages.sort(function(a, b) {
  return a - b
})
// => [9, 18, 21, 24, 35, 41]
const unsorted = ['d', 'd', 'h', 'r', 'v', 'z', 'f', 'c', 'g'];
const sorted = unsorted.sort();

console.log(sorted);
//["c", "d", "d", "f", "g", "h", "r", "v", "z"]


const unsortedNums = [45, 56, 3, 3, 4, 6, 7, 45, 1];
const sortedNums = unsortedNums.sort((a, b) => {
	return a - b;
});

console.log(sortedNums);
//[1, 3, 3, 4, 6, 7, 45, 45, 56]