sortCharactersByFrequency.js

function frequencySort(string = '') {
  const charFreqMap = {};
  for (let i = 0; i < string.length; i++) {
    const char = string[i];
    const isCharInCharMap = Boolean(charFreqMap[char]);
    charFreqMap[char] = isCharInCharMap ? charFreqMap[char] + 1 : 1;
  }

  const charArray = [];
  for (let char in charFreqMap) {
    const frequency = charFreqMap[char];
    const extrapolatedString = char.repeat(frequency);
    charArray.push(extrapolatedString);
  }
  charArray.sort((a, b) => b.length - a.length);

  return charArray.join('');
};