Why does sorting a JS array of numbers with < work?

Question

When sorting an array of numbers in JavaScript, I accidentally used < instead of the usual - -- but it still works. I wonder why?

Ex

Answer 1

If we analyze what's being done, it seems that this is mostly luck as in this case, 3 and 2 are considered to be "the same" and should be interchangeable. I suppose in such cases, the JS engines keep the original order for any values that have been deemed equal:

let a = [1, 3, 2, 4];
a.sort((n1, n2) => {
  const result = n1 < n2;
  if (result < 0) {
    console.log(`${n1} comes before ${n2}`);
  } else if (result > 0) {
    console.log(`${n2} comes before ${n1}`);
  } else {
    console.log(`${n1} comes same position as ${n2}`);
  }
  return result;
})

console.log(a);

As pointed out in the comments, this isn't guaranteed to work ([1,2,1,2,1,2,1,2,1,2,1,2] being a counter-example).