Return true if two strings are anagrams of one another

isAnagram.js

const isAnagram = (str1, str2) => {
  
  if (str1.length !== str2.length) return false;
  
  const map = new Map();
  
  for (let char of str1) {
    const count = map.has(char) ? map.get(char) + 1 : 1;
    map.set(char, count);
  };
  
  for (let char of str2) {
    if (!map.has(char)) return false;
    const count = map.get(char) - 1;
    if (count === 0) {
      map.delete(char);
      continue;
    };
    map.set(char, count);
  };
  
  return map.size === 0;

};