My Solution to Caesar's Cipher in TypeScript: I had to set to JS to get syntax highlighting

ceasar.js

function caesarCipher(phraze: string, offBy: number): string {
  function hasLowerCase(str: string): boolean {
    return /[a-z]/.test(str);
  }
  function hasUpperCase(str: string): boolean {
    return /[A-Z]/.test(str);
  }
  // Here's that alphabet string
  const aToZ = "abcdefghijklmnopqrstuvwxyz";
  const uppercaseAtoZ = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

  // Loop over the offBy value if it's greater than 26
  // until it's less than 26
  while (offBy > 26) {
    offBy -= 26;
  }

  // Loop over that string
  const encryptedString = phraze.split("").map((current, i) => {
    // Hold lowercase boolean
    let isLowerCase: boolean;

    // If it's not a letter just return the char
    if (hasLowerCase(current.toString())) {
      isLowerCase = true;
    } else if (hasUpperCase(current.toString())) {
      isLowerCase = false;
    } else {
      return current;
    }

    // Get index from the alphabet
    let locationIndex = aToZ.indexOf(current.toLowerCase());

    // logic to make sure it's under 26 and a letter
    if (isLowerCase && locationIndex + offBy <= 25) {
      return aToZ[locationIndex + offBy];
    } else if (!isLowerCase && locationIndex + offBy <= 25) {
      const cryptoLetterIndex = locationIndex + offBy;
      return uppercaseAtoZ[cryptoLetterIndex];
    } else if (isLowerCase && locationIndex + offBy > 25) {
      return aToZ[locationIndex + offBy - 25];
    } else if (locationIndex + offBy > 25 && !isLowerCase) {
      return aToZ[locationIndex + offBy - 25].toLocaleUpperCase();
    } else {
      return current;
    }
  });
  return encryptedString.join("");
}