link: https://leetcode.com/problems/longest-substring-without-repeating-characters/description/
> Given a string, find the length of the longest substring without repeating characters.
Examples:
```
Given "abcabcbb", the answer is "abc", which the length is 3.
Given "bbbbb", the answer is "b", with the length of 1.
Given "pwwkew", the answer is "wke", with the length of 3. Note that the answer must be a substring, "pwke" is a subsequence and not a substring.
```
# JavaScript
```js
/**
* @param {string} s
* @return {number}
*/
var lengthOfLongestSubstring = function(s) {
if (s === "") {
return 0;
}
let subStr = [];
let maxStr = [];
s.split("").forEach((c, i) => {
const pos = subStr.indexOf(c);
// if character already exists
if (pos !== -1) {
// start tracking from just after old occurance of character
subStr = subStr.slice(pos + 1, i);
}
// add new character
subStr.push(c);
// check if current is new longest
if (subStr.length > maxStr.length) {
maxStr = subStr.join("");
}
});
return maxStr.length;
};
```
