First Unique Character in a String

firstUniqChar.js

const firstUniqChar = (s) => {
   let res = new Map();
    [...s].forEach((i) => {
        res.has(i) ? res.set(i, res.get(i) + 1) : res.set(i, 1)
    })
 
    
    for (const [key, value] of res.entries()) {
        if(value === 1) {
            return s.indexOf(key)
        }
    }
    
    return -1;
};