SOURCE

var isAnagram = function(s, t) {
    let slen = s.length;
        let tlen = t.length;

        if (slen != tlen) {
            return false;
        }

        let totalchars = 26;
        let asciistart = 97;
        let ary = new Array(26);

        for (let i = 0; i < totalchars; i++) {
            ary[i] = 0;
        }

        for (let i = 0; i < slen; i++) {
            ary[s.charCodeAt(i) - asciistart]++;
            ary[t.charCodeAt(i) - asciistart]--;            
        }

        for (let i = 0; i < totalchars; i++) {
            if (ary[i] !== 0) {
                return false;
            }
        }

        return true;
};
console.log(isAnagram("aacc", "ccac"));