Truncate a String: solution proposed better than Advanced FCC Solution?

JavaScript
1

Tell us what’s happening:
This is the FCC Advanced:

function truncateString(str, num) {
  if (str.length <= num) {
    return str;
  } else {
    return str.slice(0, num > 3 ? num - 3 : num) + '...';
  }
}

I just wanna hear your thoughts about the Title question?
The proposed solution:
1)It should be a bit faster
2) use two methods instead of nested conditionals
3) is more readable

Your code so far


function truncateString(str, num) {
  let x;
  num < str.length ? x = str.slice(0, num).concat("...") : x = str.slice(0, num)
  return x
}

truncateString("A-", 1) // --> A...

Your browser information:

User Agent is: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/75.0.3770.142 Safari/537.36 OPR/62.0.3331.119.

Link to the challenge:

2

the solution in the guide is just wrong, it is about an old version of the challenge

your algorithm does a different thing, you can’t really compare them