First Unique Character in a String

Given a string s, find the first non-repeating character in it and return its index. If it does not exist, return -1.

Example:

Input: s = "leetcode"

Output: 0

Constraints:

1 <= s.length <= 10^5

s consists of only lowercase English letters.

Solution in JavaScript:

var firstUniqChar = function(s) {
    let set = {}
    let uniqCharIndex = -1
    for (let i = 0; i < s.length; i++) {
        if (set[s[i]]) {
            set[s[i]].count++
        } else {
            set[s[i]] = {}
            set[s[i]].count = 1
            set[s[i]].index = i
        }
    }
    
    for (let j in set) {
        if (set[j].count === 1) {
            uniqCharIndex = set[j].index
            break
        }
    }
    
    return uniqCharIndex
};