1function lengthOfLongestSubstring(s) {
2 const set = new Set();
3 let left = 0, best = 0;
4 for (let right = 0; right < s.length; right++) {
5 while (set.has(s[right])) {
6 set.delete(s[left]);
7 left++;
8 }
9 set.add(s[right]);
10 best = Math.max(best, right - left + 1);
11 }
12 return best;
13}