/** ORIGINAL SOLUTION */
function countLetter(letter, words) {
  const regExpLetter = new RegExp(letter, 'g');
  let result = words.match(regExpLetter);
  if (result) {
    return result.length
  }
  return result;
}
function checkAnagram(firstString, secondString) {
  let dataLength = 0;
  const letterLength = firstString.length;
  if (firstString.length === secondString.length) {
    // convert all to lowercase
    const firstStringLower = firstString.toLowerCase();
    const secondStringLower = secondString.toLowerCase();
    // check if each letter have a match & same count
    for(let i = 0; i < firstStringLower.length; i++) {
      let checkedList = [];
      const baseLetter = firstStringLower[i];
      for(let j = 0; j < secondStringLower.length; j++) {
        const compareLetter = secondStringLower[j];
        const isMatchLetter = baseLetter === compareLetter;
        const isSameCountLetter = countLetter(baseLetter, firstStringLower) === countLetter(baseLetter, secondStringLower);
        if (isMatchLetter && isSameCountLetter && !checkedList.includes(baseLetter)) {
          checkedList.push(baseLetter);
          dataLength += 1;
        }
      }
    }
  }
  return dataLength === letterLength;
}