Replace All Digits with Characters

export function replaceDigits(s: string): string {
  const shift = (c: string, x: number) => {
    return String.fromCharCode(c.charCodeAt(0) + x);
  };
 
  return [...s].map((char, i) => (i % 2 === 0 ? char : shift(s[i - 1], +char))).join('');
}