en.javascript.info/1-js/02-first-steps/14-function-basics/3-min/solution.md

A solution using if:

function min(a, b) {
  if (a < b) {
    return a;
  } else {
    return b;
  }
}

A solution with a question mark operator '?':

function min(a, b) {
  return a < b ? a : b;
}

P.S. In the case of an equality a == b it does not matter what to return.