Valid Anagram

var isAnagram = function (s, t) {    if (s.length !== t.length) {        return false;    }    let countS = new Map();    let countT = new Map();    for (let start = 0; start < s.length; start++) {        countS.set(s[start], 1 + (countS.get(s[start]) ? countS.get(s[start]) : 0));        countT.set(t[start], 1 + (countT.get(t[start]) ? countT.get(t[start]) : 0));    }    for (const [key, value] of countS) {        if (countS.get(key) !== countT.get(key)) {            return false;        }    }    return true;}