Why my code lengthOfLongestSubstring() on leetcode is working perfect in console but failed after submitting?

The question is on leetcode, No 3:
https://leetcode.com/problems/longest-substring-without-repeating-characters/submissions/

Here is my code:

/**
 * @param {string} s
 * @return {number}
 */
var lengthOfLongestSubstring = function(s) {
  console.log('input', s);
  var max_length = s.length;
  var results = [];
    
    var isDupCheck = function(arr){
        var s = [];
        var hasDup = false;
        arr.forEach(function(el){
            if (!s.includes(el)) {
                s.push(el);
            } else {
                hasDup = true;
            }

        })
        return hasDup;
    }

    
  for (var j = 0; j<max_length; j++)
    for (var i = 1; i<max_length; i++) {
      var substr = s.substr(j, i);
      var isDup = isDupCheck(substr.split(''));
      if (!isDup) {
          results.push(substr);
      }
  }
  var length = 0;
  var picked;
  console.log("results:", results);
  results.forEach(function(el){
      if (el.length > length) {
          length = el.length;
          picked = el;
      }
  });
  var picked_length = picked.split('').length;
  console.log(picked_length); // expected output
  return 5; // If I comment this line, there will be an ERROR.
  return picked_length;
};

The console.log(picked_length) outputs exactly the expected solve. But if I return the picked_length, then submit, there will be an error:

Line 42 in solution.js
  var picked_length = picked.split('').length;
                             ^
    TypeError: Cannot read properties of undefined (reading 'split')
        Line 42: Char 30 in solution.js (lengthOfLongestSubstring)
        Line 57: Char 19 in solution.js (Object.<anonymous>)
        Line 16: Char 8 in runner.js (Object.runner)
        Line 48: Char 26 in solution.js (Object.<anonymous>)
        at Module._compile (node:internal/modules/cjs/loader:1101:14)
        at Object.Module._extensions..js (node:internal/modules/cjs/loader:1153:10)
        at Module.load (node:internal/modules/cjs/loader:981:32)
        at Function.Module._load (node:internal/modules/cjs/loader:822:12)
        at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:81:12)
        at node:internal/main/run_main_module:17:47

>Solution :

My guess is that they’re giving you an empty string, based on their constraints –

0 <= s.length <= 5 * 104

Looking at your code here –

var picked;
console.log("results:", results);
results.forEach(function(el) {
  if (el.length > length) {
    length = el.length;
    picked = el;
  }
});

If there are no results, then you’re not assigning anything to picked. If you initialize it to an empty string, the problem should go away.

Edit

For what it’s worth, I couldn’t help but try the problem myself. It’s deceiptively difficult to solve without violating their constraints for time/memory, but this was the best solution I could come up with… it works well because a javascript Set guarantees iteration order, but the lookup time for an element should be faster than using an array:

/**
 * @param {string} s
 * @return {number}
 */
var lengthOfLongestSubstring = function(s) {
    if (!s?.length) return 0;
    
    let longest = 0;
    let seenChars = new Set();
    
    for (const char of s) {
        if (seenChars.has(char)) {
            longest = Math.max(longest, seenChars.size);
            
            for (const seenChar of seenChars) {
                seenChars.delete(seenChar);
                if (seenChar === char) break;
            }
        }
        
        seenChars.add(char);
    }            
    
    return Math.max(longest, seenChars.size);
};