isAnagram = (s, t, map = new Map()) => {
    const isEqual = s.length === t.length;
    if (!isEqual) return false;

    addFrequency(s, map);      /* Time O(N) | Space O(1) */
    subtractFrequency(t, map); /* Time O(N) | Space O(1) */

    return checkFrequency(map);/* Time O(N) */
}
Hash Map - Frequency Counter
Time O(N) | Space O(1)
https://leetcode.com/problems/valid-anagram/
@param {string} s
@param {string} t
@return {boolean}