function hexStringToRGB (hexString) {
  let r = hexString.substring(0, 2)
  let g = hexString.substring(2, 4)
  let b = hexString.substring(4, 6)

  r = parseInt(r, 16)
  g = parseInt(g, 16)
  b = parseInt(b, 16)
  const obj = { r, g, b }

  return obj
}

console.log(hexStringToRGB('ffffff'))