How to determine if a string is a permutation of another string in JavaScript

JavaScript, algorithms, strings

Here is one way to determine whether a string is a permuation of another string in JavaScript.
Space complexity: O(n)
Time complexity: O(n)

Another approach could involve sorting the two strings and iterating through the length of one of the strings.

checkPermutationTry in REPL
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function checkPermutation(string1, string2) {
  const charCount1 = getCountMap(string1);
  const charCount2 = getCountMap(string2);
  
  return charCountsMatch(charCount1, charCount2);
}
function getCountMap(string) {
  return string.split('').reduce((map, char) => {
    (map[char] && map[char]++) || (map[char] = 1);
    return map;  
  }, {});
}
function charCountsMatch(map1, map2) {
  if (Object.keys(map1).length !== Object.keys(map2).length) return false;
  
  for (const key in map1) {
    if (map1[key] !== map2[key]) return false;  
  }
  return true;
}
// ========
function checkPermutationBitwise(string1, string2) {
  let signature1, signature2 = 0;
  
  string1.split('').forEach((char) => {
    signature1 ^= char.charCodeAt(0);  
  });
  
  string2.split('').forEach((char) => {
    signature2 ^= char.charCodeAt(0);
  });
  
  return signature1 === signature2;  
}
// checkPermutation = checkPermutationBitwise // Uncomment to use bitwise version

Tests can be found at REPL.it