Why my method not returning the string with char case toggled

This is my method, it was returning the same string as the input.
for ex: toggleEveryCharCases(‘character’) => ‘character’

Please answer me guys…

export function toggleEveryCharCases(str: string): string {
  const strArr = str.split('');

  for (let i = 0; i < strArr.length; i++) {
    if (strArr[i] >= 'A' && strArr[i] <= 'Z') strArr[i] = strArr[i].toLowerCase();
    else if (strArr[i] >= 'a' && strArr[i] <= 'z') strArr[i] = strArr[i].toUpperCase();
  }

  return strArr.join('');
}

I have tried my best. I want to get the char case togggled string