Reverse Prefix of Word

export function reversePrefix(word: string, ch: string): string {
  function reverseString(s: string) {
    return [...s].reverse().join('');
  }
 
  const i = word.indexOf(ch);
  if (i === -1) {
    return word;
  }
  return reverseString(word.substring(0, i + 1)) + word.substring(i + 1);
}